Palbociclib Therapy Research Articles

Proton pump inhibitors decrease efficacy of palbociclib in patients with metastatic breast.

The objective of this investigation was to assess the impact of concurrent proton pump inhibitors (PPIs) on progression-free survival (PFS) in patients with hormone receptor-positive and HER2-negative metastatic breast cancer (mBC) who received palbociclib as first-line or successives therapy. A retrospective observational study was conducted, enrolling patients diagnosed with estrogen receptor-positive, human epidermal growth factor receptor 2-negative mBC, and eligible for palbociclib treatment. Patients were categorized as "concurrent PPIs" if they received PPIs for at least two-thirds of the palbociclib therapy duration, and as "no concurrent PPIs" if they did not receive PPIs during the course of palbociclib treatment. A total of 165 patients were included in the study. Among first-line patients treated with palbociclib, those using concurrent PPIs exhibited a PFS of 8.88 months, while patients using palbociclib without concurrent PPIs had a PFS of 67.81 months (p < 0.0001). In second-line or subsequent treatments, patients on palbociclib with concurrent PPIs had a PFS of 7.46 months, whereas those using palbociclib without concurrent PPIs had a PFS of 17.29 months (p = 0.122). This study demonstrates that the concurrent use of PPIs in mBC patients receiving palbociclib negatively affects PFS, particularly in the first-line setting. Nevertheless, further investigation is warranted to explore the impact of PPIs on cycle-dependent kinase 4/6 inhibitors.

Results of a retrospective study on the efficacy and safety of alpelisib in patients with HR+/HER2- metastatic breast cancer in real-world clinical practice.

e13058 Background: The combination of alpelisib and fulvestrant is an optimal therapy option for patients with hormone receptor-positive (HR+), HER2-negative (HER2–) metastatic breast cancer with PIK3CA gene mutations. The aim of this work to retrospectively analyze the efficacy and safety of alpelisib in real-world clinical practice in patients with pre-treated luminal HER2– negative metastatic breast cancer. Methods: The study included an analysis of 33 patients with widespread luminal HER2- negative breast cancer with detected PIK3CA gene mutation. The median age was 57 ± 13 months (95% CI 52-62). In 12 (36.4%) patients, the PIK3CA gene mutation was detected in exon 9, and in 21 (63.6%) – in exon 20. Alpelisib was prescribed to pre-treated patients in different lines. Most women (32/33; 97%) had received ET combined regimens with CDK4/6 inhibitors before starting alpelisib therapy: 14 (42.4%) patients underwent palbociclib therapy in combination with fulvestrant; 4 (12.1%) – palbociclib with aromatase inhibitors; 13 (39.5%) – ribociclib in combination with fulvestrant; 1 (3.0%) – ribociclib with aromatase inhibitors. It is important to note that 63.6% of patients had previous progression on fulvestrant monotherapy and 72.7% on aromatase inhibitor therapy. Patients with luminal B-subtype of breast cancer dominated - 72.7% (24/33). Results: The median overall survival (OS) in this study was 14 ± 2.5 months (95% CI: 9-18.9), and the median progression-free survival (PFS) was 6 ± 2.7 months (95% CI: 0.7-11.3). The rate of objective response was 30.3%, and prolonged disease stabilization was observed in 24.2% of cases. Prognostic factors were brain metastases (increasing the risk of death by 18 times) and discontinuation of the drug for any reason (increasing the risk of death by 8 times). It should be noted that the main reason for discontinuation or disruption of the drug's timing was unmanageable toxicity. All patients registered adverse events of varying degrees, with 21 (63.6%) patients experiencing hyperglycemia (grade 3-4 – 30.3%) and 14 (42.4%) patients experiencing skin toxicity (grade 3-4 – 15.2%). In the SOLAR-1 study, the frequency of hyperglycemia was comparable (64.8%), and rash was noted in a third of all patients, which is comparable to our data. Conclusions: The results of using alpelisib with fulvestrant confirm its effectiveness in real-world clinical practice in patients with pre-treated HR+HER2- negative widespread breast cancer with the presence of somatic PIK3CA gene mutation. Brain involvement is an unfavorable prognostic factor in patients with PIK3CA mutation and increases the risk of death by 18 times, requiring the need to optimize the therapeutic algorithm, including through radiation methods. Discontinuation of the drug, which increases the risk of death by 8 times.

Abstract PO1-25-08: Evaluating the role of CDK4/6 inhibition on STAT3 activation in a transgenic mouse model of HER2-positive breast cancer

Abstract Background: The human epidermal growth factor receptor 2 (HER2) is a receptor tyrosine kinase overexpressed in approximately 20-25% of breast cancers with varying biological differences according to hormone receptor (HR) positive status. Combination of chemotherapy with dual HER2 blockade and endocrine therapy (adjuvant) or CDK4/6 inhibitor (CDK4/6i) therapy (metastatic) is standard of care for HER2-positive/HR-positive breast cancer. However, de-escalation of chemotherapy remains of significant interest given associated toxicities and, as a result, alternative therapeutic strategies are needed. One such strategy is targeting the signal transducer and activator of transcription 3 (STAT3) which is constitutively activated in the HER-2 positive setting. Moreover, there is preclinical evidence to suggest that phosphorylated STAT3 (pSTAT3) induces overexpression of cyclin D1 (CCND1), which along with CDK4 may mediate resistance to targeted therapy for HER2-positive breast cancer. However, it is unclear if pSTAT3 plays a significant role in tumorigenesis or the development of resistance to therapy in HER2-positive disease. We aim to evaluate the effect of CDK4/6i therapy with palbociclib on tumor growth in an inducible transgenic HER2-positive mouse model and the impact on pSTAT3 and cyclin D1 levels. Methods: Using an inducible transgenic mouse mammary tumor virus (MMTV) model of HER2-positive breast cancer, we evaluated STAT3 phosphorylation in tumors driven by HER2 expression in addition to the impact of CDK4/6 inhibition with palbociclib on tumorigenesis and pSTAT3 activation. To model tumor recurrence, doxycycline was withdrawn from tumor bearing mice and tumor regression was observed. Subsequently, the mice developed recurrent mammary tumors. Given recurrent tumors in this model are driven by a HER2-independent mechanism, we examined expression of cell cycle proteins together with STAT3 phosphorylation to determine association with recurrence. Result: In addition to expressing HER2, the primary tumors expressed estrogen receptor (ERα), Rb, cyclin D1, and CDK4/6 proteins. STAT3 phosphorylation was also observed. Treatment with palbociclib decreased Rb phosphorylation and decreased tumor growth compared to vehicle treated mice (%TGI 79.37% after 21 days). Furthermore, pSTAT3 levels were not altered with palbociclib therapy. When recurrent tumors were analyzed, they lacked HER2 expression but expressed cyclin D1 and CDK4/6 supporting that tumor growth is driven by cyclin D1/CDK4 pathway. Recurrent tumors also demonstrated pSTAT3 despite lack of HER2 expression suggesting that STAT3 phosphorylation in the recurrent tumors is mediated by an alternative mechanism, potentially the CDK4/6 pathway. Conclusion: We demonstrate STAT3 activation in a mouse model of HER2 driven breast cancer and show persistent activation in recurrent tumors lacking HER2 expression rendering them resistant to HER2-targeted therapy. We also demonstrate the anti-tumor effect of palbociclib in primary tumors with HER2-dependent proliferation. Taken together, our findings suggest that pSTAT3 is a viable therapeutic target and provides the rationale for combination therapy with CDK4/6 inhibition using palbociclib and STAT3 inhibition with a novel STAT3 inhibitor in HER2-positive breast cancer. This therapeutic approach may represent a potential chemotherapy de-escalation strategy. Citation Format: Taiwo Adesoye, Linjie Luo, Tuyen Bui, Serena Kim, Hannah Wingate, Debu Tripathy, Kelly Hunt, Khandan Keyomarsi. Evaluating the role of CDK4/6 inhibition on STAT3 activation in a transgenic mouse model of HER2-positive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-25-08.

Measures of functional status in older patients treated with palbociclib for advanced breast cancer

IntroductionLimited data are available on the effects of treatment for advanced breast cancer (ABC) in older patients because this population has limited enrollment in clinical trials. Data generated from the prospective, noninterventional POLARIS study of patients with hormone receptor-positive/human epidermal growth factor receptor 2–negative ABC may help bridge the gap in our understanding of the tolerability and outcomes in this vulnerable population. Materials and MethodsWe evaluated measures of geriatric impairments and activities of daily living in patients with ABC aged ≥70 years in POLARIS to evaluate the change within six months of palbociclib initiation. Geriatric impairments and activities of daily living (functional) status were assessed using the Geriatric 8 (G8) and Activities of Daily Living (ADL) screening tools. The G8, ADL, and Eastern Cooperative Oncology Group performance status (ECOG PS) scores were assessed at baseline and month six through end of treatment with palbociclib. ECOG PS scores were also stratified by G8 and ADL score severity subgroups (G8: ≤14 = impaired subgroup; >14 = not at all impaired subgroup; ADL: <18 = dependent subgroup, 18 = independent subgroup). ResultsAt data cutoff in November 2020, of 1282 POLARIS patients of all ages, 287 (22.4%) were ≥ 70 years old and completed ≥6 months of palbociclib therapy. At baseline, 117 (45%; n = 260) of these patients had an ECOG PS score of 0, 143 (55%; n = 260) had ECOG PS score > 0, 248 (86%) had G8 scores (mean [SD] 13.6 [2.14]), and 256 (89%) had ADL scores (17.7 [1.03]) among the available 287 patients. At six months, 102 (40%; n = 255) had an ECOG PS score of 0, 153 (60%; n = 255) had ECOG PS score > 0, 198 (69%) had G8 scores (13.6 [1.99]), and 211 (74%) had ADL scores (17.6 [1.22]) among the 287 available patients. There was no mean change (standard deviation) from baseline to 6 months in mean ECOG PS scores (0.0 [0.61], P = 0.24), G8 scores (0.0 [2.17], P = 0.89), or ADL scores (0.0 [1.00], P = 0.62). DiscussionIn this subgroup analysis of older patients with ABC from POLARIS, functional status and impairment outcomes were preserved in older patients receiving palbociclib. G8, ADL, and ECOG PS scores were generally maintained during the first six months of palbociclib therapy.ClinicalTrials.govidentification number.NCT03280303

Evaluation of Electrocardiographic Repolarization Parameters in Patients who Received Ribociclib and Palbociclib Therapy

Abstract Introduction: Ribociclib and palbociclib are the inhibitors of cyclin-dependent kinase (CDK) 4/6 activity which have been used in the treatment of metastatic hormone receptor (HR)-positive, human epidermal growth factor receptor 2-negative breast cancer. QT interval prolongation has been the main reported adverse effect in Phase III trials of ribociclib and palbociclib therapy. In the present study, we aimed to evaluate electrocardiographic (ECG) changes in patients who received palbociclib and ribociclib therapy. Materials and Methods: Sixty women with metastatic HR-positive, human epidermal growth factor-2-negative breast cancer were included in the study. Baseline ECG and echocardiographic examinations of these patients were done. Second control electrocardiogram was obtained on the 14th day of first-cycle therapy. PR interval, corrected QT (QTc) interval, QT dispersion (QTD), and QRS duration were calculated. Results: Heart rate, PR interval, QRS, QT, QTc, QTD, and corrected QTD duration did not differ before and after CDK 4/6 treatment. Two patients who received ribociclib and palbociclib treatment had basal QTc duration higher than 450 ms (458 ms and 465 ms, respectively). The 14th-day QTc intervals of these patients were found to be 318 ms and 406 ms, respectively. After CDK 4/6 treatment, only two patients had QTc interval of 469 ms and 507 ms. The mean change of QTc interval before and during the 14th day of CDK 4/6 therapy was 7.38 ± 35.049 ms. When palbociclib and ribociclib treatments were analyzed separately, the baseline and 14th day of QTc interval were 415 ± 31.5 versus 428.11 ± 24.52 and 416.13 ± 26.05 versus 420.07 ± 31.32 ms, respectively. Conclusions: Ribociclib and palbociclib treatment was associated with a small statistically insignificant increase in QTc interval. Physicians should be aware of the side effect of these treatments.

Treatment of palbociclib in hormone receptor positive breast cancer: a real-world study and efficacy prediction model

Objective: To summarize the clinical use of palbociclib and evaluate its efficacy and safety in hormone-receptor (HR)-positive advanced breast cancer patients. Methods: We retrospectively analyzed data from 66 HR-positive metastatic breast cancer patients treated with palbociclib and endocrine therapy at the Department of Oncology in the First Affiliated Hospital with Nanjing Medical University between 2018 and 2020. We evaluated the factors affecting the efficacy of palbociclib using Kaplan-Meier method and Log-rank test for survival analysis and Cox regressions for multivariate analysis. Nomogram model was built for predicting prognosis among HR-positive breast cancer patients who received palbociclib. Concordance index (C-index) and calibration curve were used for internal validation to assess the predictive ability and conformity of the model. Results: Of the 66 patients treated with palbociclib, 33.3%(22), 42.4%(28) and 24.2%(16) patients were treated without endocrine therapy, first-line endocrine therapy, second-line or above endocrine therapy after recurrence, respectively. 36.4%(24) patients had hepatic metastasis, 16.7% (11) patients were sensitive to previous endocrine therapy, 27.3%(18/66) patients had primary resistance to endocrine therapy, while 56.1% (37) patients had secondary resistance to endocrine therapy. The overall response rate was 14.3% (95% CI: 6.7%, 25.4%) and clinical benefit rate was 58.7% (95% CI: 45.6%, 71.0%). Better clinical outcomes were associated with non-hepatic metastasis (P=0.001), sensitive/secondary resistant to previous endocrine therapy (P=0.004), no or only one line of chemotherapy for metastatic breast cancer (P=0.004), recent pathological confirmation of immunohistochemical analysis (P=0.025). Hepatic metastasis (P=0.005) and primary resistance to endocrine therapy (P=0.016) were the independent risk factors of progression free survival. The C-index of predictive probability for the nomogram constructed from the patient clinical characteristics (whether liver metastasis, whether primary endocrine resistance, lines of chemotherapy after metastasis, lines of endocrine therapy, number of metastatic sites, and time to last immunohistochemistry) to predict the progression-free survival at 6 and 12 months for patients was 69.7% and 72.1%, respectively. The most common adverse events were hematologic toxicities. Conclusions: Our report indicates that palbociclib combined with endocrine therapy for HR-positive recurrent metastatic breast cancer is effective and safe; patients with hepatic metastases and primary resistance to endocrine therapy have worse prognoses and are independent risk factors for progression after palbociclib therapy. The constructed nomogram could help predict the survival and guide the use of palbociclib.

Palbociclib Adherence and Persistence in Patients with Hormone Receptor Positive/Human Epidermal Growth Factor Receptor 2 Negative (HR+/HER2-) Metastatic Breast Cancer

To assess adherence and persistence with palbociclib therapy in patients with HR+/HER2- metastatic breast cancer (mBC) in a US real-world setting. This retrospective study evaluated palbociclib dosing, adherence, and persistence using commercial and Medicare Advantage with Part D claims data from the Optum Research Database. Adult patients with mBC who had continuous enrollment 12 months prior to mBC diagnosis and initiated first-line palbociclib with aromatase inhibitor (AI) or fulvestrant between 02/03/2015 and 12/31/2019 were included. Demographic and clinical characteristics, palbociclib dosing and dose changes, adherence (medication possession ratio [MPR]), and persistence were measured. Adjusted logistic and Cox regression models were used to examine demographic and clinical factors associated with adherence and discontinuation. Patients (n = 1066) with a mean age of 66 years were included; 76.1% received first-line palbociclib+AI and 23.9% palbociclib+fulvestrant. Most patients (85.7%) initiated palbociclib at 125 mg/day. Of the 34.0% of patients with a dose reduction, 82.6% reduced from 125 to 100 mg/day. Overall, 80.0% of patients were adherent (MPR), and 38.3% discontinued palbociclib during a mean (SD) follow-up of 16.0 (11.2) and 17.4 (13.4) months, for palbociclib+fulvestrant and palbociclib+AI, respectively. Annual income below $75,000 was significantly associated with poor adherence. Older age (age 65-74 years (hazard ratio [HR] 1.57, 95% CI, 1.06, 2.33), age ≥75 years (HR 1.61, 95% CI: 1.08, 2.41)) and bone-only metastatic disease (HR 1.37, 95% CI, 1.06, 1.76) were significantly associated with palbociclib discontinuation. In this real-world study, >85% of patients started palbociclib at 125 mg/day and 1 in 3 had dose reductions during the follow-up. Patients were generally adherent and persistent with palbociclib. Older age, bone-only disease, and low-income levels were associated with early discontinuation or non-adherence. Further studies are needed to understand the associations of clinical and economic outcomes with palbociclib adherence and persistence.

Abstract P1-13-22: Establishment and characterization of two ER+/HER2- XPDX models developed sequentially before and after acquired resistance to the CDK4/6 inhibitor palbociclib from a patient with metastatic breast cancer

Abstract Background: Several CDK4/6 inhibitors have recently been approved in combination with letrozole or fulvestrant in hormone receptor-positive breast cancer. Although this combination therapy has been found effective in some patients, resistance often develops. To aid in developing new therapies for CDK4/6i-resistant breast cancer and better understand potential resistance mechanisms, we established two XenoSTART Patient-Derived Xenograft (XPDX) models representing ER+/HER2- breast cancer from tissue samples collected seventeen months apart from the same patient before and after palbociclib therapy. These models designated ST4887 and ST4887B were developed and characterized for receptor expression, genomic alterations, and in vivo drug sensitivities toward multiple chemotherapies and targeted agents, including CDK4/6i and fulvestrant. Methods: Models ST4887 and ST4887B were established from metastatic samples collected from a Caucasian female with ER+/HER2- metastatic breast cancer; ST4887 was collected at age 38 from a femur mass biopsy following several treatment regimens including paclitaxel/doxorubicin/cyclophosphamide, radiation and tamoxifen. ST4887B was collected at age 39 from a liver biopsy following treatment with palbociclib/letrozole then palbociclib/fulvestrant, and finally ixabepilone/capecitabine. Both were grown subcutaneously in female athymic nude mice supplemented with exogenous estradiol. The resulting models were passaged, and receptor expression confirmed immunohistochemically; genomic analysis, including WES and RNAseq, was performed to further characterize models. For in vivo studies, both models were evaluated using several chemotherapy and targeted agents alone and in combination including cisplatin, docetaxel, CDK4/6i, fulvestrant, letrozole, olaparib, niraparib, and sacituzumab. In vivo study endpoints included tumor volume and time from treatment initiation with %T/C values and tumor regression reported at study completion; a T/C of ≤ 20% versus control was considered sensitive. Tumor regression (%T/C=&amp;lt; 0) versus Day 0 tumor volume was also reported. Results: ST4887 and ST4887B retained comparable receptor expression (ER=3+/HER2=1+) over tested passages with similar histology compared to archival clinical samples. DNA/RNA sequencing identified several conserved variants including a somatic BRCA2 truncation (BRCA2Y2660*); transcriptomic analysis revealed upregulation of several related genes but no notable fusions. In vivo, both models were insensitive to cisplatin or docetaxel, however ST4887 but not ST4887B was sensitive to fulvestrant or CDK4/6i therapies, although abemaciclib demonstrated some activity toward ST4887B. PARP inhibitors were active toward ST4887 and to a lesser extent ST4887B, while sacituzumab did not have a significant effect on either model. Conclusion: We established and characterized two XPDX models from the same patient before and after acquired resistance to the CDK4/6i palbociclib. Both models were found to retain receptor status and drug sensitivities similar to the patient at the time of sample collection. These models can be utilized as a valuable tool in better understanding acquired resistance to palbociclib. Citation Format: Ashwin Varma, Johnnie Flores, Alyssa Simonson, Anna Stackpole, Kyriakos P. Papadopoulos, Amita Patnaik, Drew Rasco, Muralidhar Beeram, Marisa Sandera, Michael Wick. Establishment and characterization of two ER+/HER2- XPDX models developed sequentially before and after acquired resistance to the CDK4/6 inhibitor palbociclib from a patient with metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-13-22.

Cyclin-Dependent Kinase 4/6 Inhibitor Palbociclib Synergizes with BH3-Mimetics in Experimental Models of Relapsed/Refractory Mantle Cell Lymphoma

Introduction: Mantle cell lymphoma (MCL) is an aggressive subtype of B-cell non-Hodkin lymphomas characterized by cyclin D1 upregulation. The complex of upregulated cyclin D1 and cyclin-dependent kinases (CDK) 4 and 6 deregulates G1/S cell cycle transition of malignant lymphocytes, which represents a rationale druggable target. Palbociclib, a CDK 4/6 inhibitor approved for the therapy of patients with breast cancer, demonstrated single-agent clinical activity in relapsed/refractory (R/R) MCL. BH3-mimetics bind to an anti-apoptotic BCL-2 proteins (Bcl-2, Bcl-xL or Mcl-1) and thereby block their anti-apoptotic function. Specific Bcl-2 inhibitor venetoclax, the only FDA approved member of BH3-mimetics, is currently being tested in numerous clinical trials in hematological malignancies. Interestingly, the combination of palbociclib and venetoclax showed promising results in patients with breast cancer but has never been tested in patients with MCL. Methods: Experimental therapy aimed at inhibition of CDK by palbociclib and anti-apoptotic BCL-2 proteins using venetoclax, S63845 and A1155463 was performed on nine MCL cell lines and four patient-derived xenograft (PDX) models from patients with R/R MCL. Mitochondrial priming to apoptosis was assessed by BH3 profiling. Expression of selected cell cycle regulators, pro-, and anti-apoptotic proteins was evaluated before and after exposure to palbociclib by western blotting both in vitro and in vivo. Spectrum of BCL-2-bound BH3-only proteins were detected by immunoprecipitation of MCL tumors ex vivo 24 and 48 hours after start of palbociclib therapy (compared to tumors obtained from untreated controls). Impact of palbociclib on energo-metabolic pathways in MCL cells was measured by SeaHorse assay. MCL clones with knockdown or overexpression of CDKN2A, MYC, CDK4 and RB1 were used to evaluate impact of these aberrations on the sensitivity to palbociclib (and venetoclax). Results: Synergistic effect of palbociclib was observed in combination with all BH3-mimetics (venetoclax, S63845 and A1155463) in vitro, and confirmed in vivo on PDX R/R MCL models using venetoclax, as the only FDA approved member. Exposure of MCL-bearing mice to palbociclib induced downregulation of D-type cyclins, cyclin A, Rb1 and Mcl-1 proteins. Even though single-agent palbociclib had limited cytotoxic (proapoptotic) effect, it increased pro-apoptotic mitochondrial priming. Immunoprecipitation experiments revealed that the level of Bim bounded to Bcl-2 was not significantly changed, and the level of Bim bounded to Bcl-xL was increased 24 hours after exposure to palbociclib. Curiously, palbociclib significantly increased level of basal and maximal oxidative phosphorylation after cultivation with MCL cells for 72 hours (but not 24 hours). Pre-treatment of MCL cells with palbociclib showed even greater synergy than simultaneous palbociclib and BH3-mimetic application. MCL cell clones with RB1 knockdown became resistant to palbociclib. Susceptibility of MCL clones with knockout of CDKN2A, overexpression of MYC, and overexpression of CDK4 to palbociclib and venetoclax was not significantly changed. Conclusion: Our data strongly support investigation of palbociclib in combination with venetoclax as an innovative treatment strategy for chemoresistant MCL patients without RB1 deletion. Although we demonstrated that palbociclib increases pro-apoptotic mitochondrial priming and induces metabolic stress, the detailed contribution of these changes to the observed synergy are under investigation.

3'-[18F]fluoro-3'-deoxythymidine ([18F]FLT) Positron Emission Tomography as an In Vivo Biomarker of inhibition of CDK 4/6-Rb pathway by Palbociclib in a patient derived bladder tumor

BackgroundSeveral new generation CDK4/6 inhibitors have been developed and approved for breast cancer therapy in combination with endocrine therapeutics. Application of these inhibitors either alone or in combination in other solid tumors has been proposed, but no imaging biomarkers of response have been reported in non-breast cancer animal models. The purpose of this study was to evaluate 3'-[18F]fluoro-3'-deoxythymidine ([18F]FLT) Positron Emission Tomography (PET) as in vivo biomarker of response to palbociclib in a non-breast cancer model.MethodsTwenty-four NSG mice bearing patient derived xenografts (PDX) of a well-characterized bladder tumor were randomized into 4 treatment groups: vehicle (n = 6); palbociclib (n = 6); temozolomide (n = 6); and palbociclib plus temozolomide (n = 6) and treated with two cycles of therapy or vehicle. Tumor uptake of [18F]FLT was determined by micro-PET/CT at baseline, 3 days, and 9 days post initiation of therapy. Following the second cycle of therapy, the mice were maintained until their tumors reached a size requiring humane termination.Results[18F]FLT uptake decreased significantly in the palbociclib and combination arms (p = 0.0423 and 0.0106 respectively at day 3 and 0.0012 and 0.0031 at day 9) with stable tumor volume. In the temozolomide arm [18F]FLT uptake increased with day 9 uptake significantly different than baseline (p = 0.0418) and progressive tumor growth was observed during the treatment phase. All groups exhibited progressive disease after day 22, 10 days following cessation of therapy.ConclusionSignificant decreases in [18F]FLT uptake as early as three days post initiation of therapy with palbociclib, alone or in combination with temozolomide, in this bladder cancer model correlates with an absence of tumor growth during therapy that persists until day 18 for the palbociclib group and day 22 for the combination group (6 days and 10 days) following cessation of therapy. These results support early modulation of [18F]FLT as an in vivo biomarker predictive of palbociclib therapy response in a non-breast cancer model.

Safety of adjuvant CDK4/6 inhibitors during the COVID-19 pandemic.

Safety of adjuvant CDK4/6 inhibitors during the COVID-19 pandemic.

Real-world effectiveness and sensitivity of palbociclib plus endocrine therapy in HR+/HER2- patients with metastatic breast cancer.

Palbociclib has shown satisfactory outcomes when combined with endocrine therapy (ET) in hormone receptor–positive and human epidermal growth factor receptor 2–negative (HR+/HER2–) metastatic breast cancer (MBC). However, data in Asia are currently scarce.This retrospective study aimed to evaluate the real-world effectiveness, sensitivity, and toxicity of palbociclib plus ET in HR+/HER2– MBC in North China. We recruited patients with HR+/HER2– MBC from August 2018 to July 2020 across 7 hospitals in North China. The primary endpoint was to evaluate progression-free survival (PFS) after initial progress on palbociclib therapy. The secondary endpoints included determining predictive biomarkers of palbociclib sensitivity and toxicity of palbociclib.A total of 54 patients were analyzed in this cohort with an estimated median follow-up time of 14.3 months. Patients who received palbociclib as a first-line treatment showed significantly prolonged PFS compared with those who received palbociclib as a second-line or beyond treatment (21.8 months vs 15.9 months vs 6.8 months) (P < .001). Besides, patients with Ki67 <30% (P = .024) and PR ≥20% (P = .041) in metastatic tumors had significantly longer PFS. The Cox proportional-hazards regression analyses proved that different lines (P = .001 in multivariate analysis), Ki67 <30% (P = .035 in multivariate analysis), and PR ≥20% (P = .045 in univariate analysis) in metastatic tumors affected PFS significantly. The most common adverse events were hematologic, with 31.48% of patients having neutropenia.Palbociclib plus ET significantly prolonged PFS for patients with HR+/HER2– MBC who received first-line therapy, with manageable toxicity. The values of Ki67 and PR in metastatic tumors may be potential predictive biomarkers of palbociclib sensitivity.

P51-3 Examination of CARG toxicity scores in palbociclib therapy for elderly patients with breast cancer

Palbociclib is proven to be effective against hormone receptor-positive, metastatic and recurrent breast cancer and is being adopted as a standard treatment. In clinical practice, elderly patients with poor general condition are at risk for adverse events of palbociclib. Four hormone receptor-positive breast cancer patients, aged 70 years and above, who received palbociclib therapy, were enrolled in this study. The toxicity risk of Grade 3-5 (G3-5) predicted through the Cancer Aging Research Group (CARG) toxicity scores, a tool for predicting adverse events in cancer chemotherapy, were retrospectively compared with the actual adverse events. The median age (range) of four patients was 76.5 (70 to 83) years. The group included one case of Stage 4 cancer and three cases of postoperative recurrence. Three patients were undergoing one endocrine therapy regimen after recurrence, while the remaining one was not undergoing any endocrine therapy regimens. None of them had a history of chemotherapy. All had CARG scores of 8 (moderate risk), and their toxicity risk of G3-5 was 59%. The actual adverse events were neutropenia: G2 one case / G3 two cases / G4 one case, thrombocytopenia: G5 one case, and anemia: G4 / one case. The G3-5 incidence, as predicted by the GARG scores, was 100%, with a concordance rate of 75% with the actual adverse events. The progression-free survival of the three patients who were able to continue therapy was 218, 444, and 377 days, respectively, showing a sufficient response period. The 85-year-old patient who started with a reduced initial dose was hospitalized four weeks after administration on account of impaired consciousness with pancytopenia. The patient died of cerebral hemorrhage three days after the administration. Palbociclib therapy in elderly patients can have serious outcomes with a moderate-to-high risk of toxicity based on the CARG score. Close follow-up is thus recommended even after dose reduction.

Demographic Characteristics and Treatment Patterns Among Patients Receiving Palbociclib for HR+/HER2- Advanced Breast Cancer: A Nationwide Real-World Experience.

BackgroundThis nationwide retrospective study reports data on the real-world use of the selective cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor palbociclib in a large population of advanced breast cancer (ABC) patients during a 2-year period in Hungary.MethodsAll patients with ABC who received palbociclib between May 1, 2017 and June 30, 2019 were included in the analysis. Patient demographic and clinical characteristics, disease-related factors and treatment patterns were examined during the early access program and in the regular reimbursement period.ResultsAltogether, 962 patients were included (mean age: 60.6 years). A total of 399 patients (41%) were treated with palbociclib plus aromatase inhibitors (P+AI), and 563 patients (59%) received palbociclib and fulvestrant (P+F). The most commonly prescribed AI was letrozole (n=359; 90%). Of those with metastatic disease (n=733; 76%), 241 patients (33%) had visceral metastases and 449 (61%) had bone-only disease. The majority of patients (79%) received palbociclib as first- or second-line therapy for ABC. The starting dose of palbociclib was 125 mg in 98% of patients; dose reductions were required in 32% of patients receiving P+AI and 31% of those treated with P+F. At the time of data collection, palbociclib therapy was ongoing in 270 patients (68%) in the P+AI group and 245 patients (44%) in the P+F group.ConclusionsThis nationwide analysis is the first to provide insights into the real-world use of palbociclib in a large patient population from a Central-Eastern European country. The findings confirm the good tolerability of palbociclib with similar dose reduction rates to those reported from registration trials.

Pre-existing effector T-cell levels and augmented myeloid cell composition denote response to CDK4/6 inhibitor palbociclib and pembrolizumab in hormone receptor-positive metastatic breast cancer

BackgroundSingle-agent pembrolizumab treatment of hormone receptor-positive metastatic breast cancer (MBC) has demonstrated modest clinical responses. Little is known about potential biomarkers or mechanisms of response to immune checkpoint inhibitors (ICIs)...

Abstract PS7-49: Assessment of patient out-of-pocket cost for palbociclib therapy in advanced breast cancer

Abstract Assessment of patient out-of-pocket cost for palbociclib therapy in advanced breast cancerBackground:Palbociclib has demonstrated improved outcomes in patients with advanced hormone receptor positive (HR+)/human epidermal growth factor 2 (HER2) negative breast cancer when used in combination with endocrine therapy 1,2. The current average wholesale price of therapy with this medication class exceeds $190,000 per year (at full dose). Financial toxicity is a major concern in the oncology population and can decrease patient quality of life and may result in non-adherence 3,4. Our objective was to describe the out-of-pocket cost burden for patients treated with palbociclib. Methods:A retrospective review of patients newly initiated on palbociclib therapy between May 5, 2018 and May 30, 2019 was completed at our institution. Patients were included if they were 18 years of age and older, newly starting palbociclib for advanced or metastatic HR+/HER2- breast cancer, had US-based insurance, and received palbociclib from our internal specialty pharmacy. Cost information was collected utilizing dispensing reports and additional patient-specific information was obtained from the EHR. Descriptive statistics were performed on the collected data. Results:A total of 44 patients were included in the cost analysis. Primary sources of coverage for these patients included commercial insurance (n=13), Medicare (n=25), and state/federal insurance (n=6). We first assessed costs with primary insurance coverage alone. The sum of all the initial cycle out-of-pocket copays after primary insurance totaled $49,108. The median individual copay was $291, the range was $0 to $2,943, and 9 of the 44 patients had no copay after the primary insurance was applied. The impact of assistance programs, which include independent grant funding, copay cards, vouchers, and secondary Medicaid plans, was significant. After applying primary insurance and aid from assistance programs, the sum of all initial cycle out-of-pocket copays reduced from $49,108 to $3,172. After assistance, 33 of the 44 patients had an initial copay cost of $0. Over 90% of the out-of-pocket total was from two patients (one each with a copay of $2,467 and $497). Ultimately, Mayo Clinic Specialty Pharmacy helped patients avoid $45,851 in first cycle out-of-pocket copays, of which $41,079 and $4,772 were for Medicare and commercially-insured patients, respectively. Copay cost by type of insurance was assessed. All patients with commercial insurance (n=13) had no actual copay for the first cycle. Medicare patients (n=25) are not eligible for copay cards and had larger pre-assistance copays compared to commercial patients (median $2,454 vs. $45). Vouchers or grants were utilized by 16 out of 25 Medicare covered patients. State/Federal insurance included 2 Tricare and 4 Medicaid patients. While ineligible for copay card assistance, the copays for these patients were low, ranging from $0-$28. Standard Medicare D plans do not have an out of pocket maximum for the year. The catastrophic phase requires an ongoing copay of 5% of the total claim cost, resulting in approximately a $600 per month copay for the remainder of the calendar year during the study period. When combined with the first cycle cost of approximately $2500, the yearly out-of-pocket cost for a patient with a standard Medicare D plan is roughly $10,000. Conclusion:Patients initiating therapy with palbociclib are commonly faced with high out-of-pocket costs. The availability, eligibility, and use of financial assistance programs are imperative in decreasing the financial toxicity. Specialty pharmacies play an important role in obtaining financial assistance which leads to decreased out-of-pocket expenses for patients. Citation Format: Allison P Golbach, Matthew D Smith, Jodi L Taraba, Karthik V Giridhar. Assessment of patient out-of-pocket cost for palbociclib therapy in advanced breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS7-49.

A multicenter analysis of treatment patterns and clinical outcomes of subsequent therapies after progression on palbociclib in HR+/HER2- metastatic breast cancer.

Introduction:Endocrine therapy and cyclin-dependent kinase (CDK) 4/6 inhibitors (CDK4/6i) are standard treatment options for hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2–) metastatic breast cancer (MBC). However, the efficacy of standard subsequent therapies after CDK4/6i-based treatment is unclear. This study aimed to examine physician practice patterns and treatment outcomes of subsequent therapies administered after progression on palbociclib therapy in clinical practice.Methods:The study included 200 patients with HR+/HER2– MBC who underwent subsequent treatments after progressing on palbociclib-based regimens in five Chinese institutions between August 2017 and April 2020. The treatment pattern, progression-free survival (PFS), overall survival (OS), and objective response rate (ORR) were reported.Results:A total of 200 patients were included, of whom 147 (73.5%) and 53 (26.5%) received subsequent chemotherapy and endocrine therapy, respectively. The frequently used monochemotherapy regimens were taxane (n = 29), capecitabine (n = 21), and vinorelbine (n = 17), while the endocrine therapy regimens were chidamide plus exemestane (n = 16) and everolimus plus exemestane (n = 9). The overall median PFS (mPFS) was 5.5 months, with no significant difference in mPFS between the chemotherapy and endocrine therapy groups (p = 0.669). However, among patients not sensitive to prior palbociclib treatment, those administered chemotherapy had significantly longer PFS than those administered endocrine therapy (p = 0.006). The mPFS with endocrine therapy after first-, second-, and subsequent-line palbociclib was 13.4, 3.1, and 4.1 months, respectively (p = 0.233); in contrast, the mPFS with chemotherapy was 7.2, 6.5, and 4.9 months after first-, second-, and subsequent-line palbociclib, respectively (p = 0.364). The median OS was not achieved. The ORR was 10.6% among the 198 patients included in the analysis.Conclusions:Physicians prefer chemotherapy over endocrine therapy for the treatment of patients with HR+/HER2– MBC who develop progression on palbociclib. Sensitivity to previous palbociclib treatment might be one of the indicators for predicting response to subsequent treatment.ClinicalTrials.gov identifier: NCT04517318

Analysis of subsequent therapy in Japanese patients with hormone receptor\u2012positive/human epidermal growth factor receptor 2\u2012negative advanced breast cancer who received palbociclib plus endocrine therapy in PALOMA-2 and -3

BackgroundIn the double-blind, phase 3 PALOMA-2 and PALOMA-3 studies, palbociclib plus endocrine therapy (ET) demonstrated significant improvement in progression-free survival versus placebo plus ET in patients with hormone receptor‒positive/human epidermal growth factor receptor 2‒negative advanced breast cancer. This analysis assessed subsequent treatment patterns after palbociclib therapy in Japanese patients enrolled in the PALOMA-2 and PALOMA-3 studies.MethodsPALOMA-2 included postmenopausal women who had not received prior systemic therapy for advanced disease. PALOMA-3 included pre- or postmenopausal women who had progressed on previous ET. Types of subsequent therapy were assessed, and treatment durations of subsequent therapy were estimated using the Kaplan–Meier method.ResultsJapanese patients were enrolled in PALOMA-2 (n = 46) and PALOMA-3 (n = 35). In both studies, the most common first subsequent therapy was ET (PALOMA-2, 77% in the palbociclib group and 75% in the placebo group; PALOMA-3, 55% and 43%, respectively), followed by chemotherapy (PALOMA-2, 18% and 8%; PALOMA-3, 32% and 57%). The median (95% CI) duration of first subsequent therapy was 6.4 (2.3‒13.9) months with palbociclib plus letrozole and 6.7 (2.8‒13.0) months with placebo plus letrozole in PALOMA-2 and 3.8 (2.4‒5.7) months with palbociclib plus fulvestrant and 9.7 (1.0‒not estimable) months with placebo plus fulvestrant in PALOMA-3.ConclusionsThe types of first subsequent therapy received by Japanese patients in the palbociclib plus ET and placebo plus ET groups were similar. Further evaluation of subsequent therapy data in the real-world setting is warranted considering the small sample size of this analysis.

Abstract 4370: Lasofoxifene alone or in combination with palbociclib as an effective treatment for therapy-resistant ER-positive metastatic breast cancer

Abstract Patients with Estrogen Receptor positive (ER+) metastatic breast cancer (MBC) are currently treated with fulvestrant, a selective estrogen receptor degrader (SERD), or a combination of fulvestrant and palbociclib, a CDK4/6 inhibitor. Approximately 25-40% of patients with MBC have activating mutations in the ERα ligand-binding domain. The two most common mutations are Y537S and D538G, which confer constitutive activity to ERα, resulting in AI/tamoxifen/fulvestrant resistance. Lasofoxifene, a selective estrogen receptor modulator (SERM), was developed for the treatment of vaginal atrophy and osteoporosis. Previous studies from this lab, performed in a mutant ERα MCF-7 xenograph MBC mouse model, showed that lasofoxifene was significantly more effective than fulvestrant at inhibiting tumor growth, as well as metastasis to the lung and liver. In the current dose/response study, we compared the efficacy of lasofoxifene + palbociclib combinations to fulvestrant + palbociclib combinations. Engineered and luciferase-GFP tagged MCF-7 Y537S cells were injected into the mammary ducts of NSG mice (MIND model) and tumor progression was monitored by live luminescence imaging of primary tumors as well as ex vivo imaging of metastatic sites at study endpoint. Our results showed that all dose combinations of lasofoxifene + palbociclib were more effective than fulvestrant + palbociclib at inhibiting primary tumor growth as well as bone, lung, liver and brain metastasis. These data strongly suggest that patients with ERα+ MBC would benefit from orally delivered lasofoxifene + palbociclib therapy and that this combination could be superior to fulvestrant + palbociclib. Citation Format: Muriel Laine, Justyna D. Kurleto, Marianne E. Greene, Linda Phung, Barry S. Komm, Geoffrey L. Greene. Lasofoxifene alone or in combination with palbociclib as an effective treatment for therapy-resistant ER-positive metastatic breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4370.

54P Establishment and characterization of luminal A breast PDX models from patients with acquired resistance to CDK 4/6 inhibitors

CDK 4/6 inhibitors have been recently approved in combination with letrozole in hormone receptor-positive breast cancer. Although this combination therapy has been found effective in some patients, resistance often develops. To aid in developing new therapies for palbociclib-resistant breast cancer and better understand resistance mechanisms, we established two PDX models from patients with luminal A breast cancer at time of progression, following acquired resistance to palbociclib therapy. Two models, designated ST3932 and ST4378, were developed in athymic nude mice and characterized for receptor expression, genomic alterations, and in vivo drug sensitivity.