Antiandrogen Withdrawal Syndrome Research Articles

Androgen Receptor Signaling Inhibitor Withdrawal Syndrome After Castration-resistant Prostate Cancer.

Androgen-deprivation therapy is an extremely effective treatment for progressive prostate cancer. Previously, the first-line treatment for progressive prostate cancer was combined androgen blockade (CAB). If the disease progressed to castration-resistant prostate cancer, the administration of androgen receptor signaling inhibitors (ARSIs) was recommended. When elevated serum prostate-specific antigen (PSA) levels are seen during CAB treatment, it is important to suspect antiandrogen withdrawal syndrome (AWS), discontinue CAB, and monitor the changes in the serum PSA levels. If a reduction in the patient's PSA levels is subsequently observed, antiandrogens should be discontinued and the patient should be followed, but if their PSA level rises they should be transitioned to ARSI treatment. Recently, there have been reports of withdrawal syndrome (WS) after ARSI treatment. With the increased use of ARSIs, such as abiraterone acetate, enzalutamide, apalutamide, and dalorutamide, it is necessary to consider ARSI WS when a patient's serum PSA level increases during ARSI treatment. Unnecessary treatment can be avoided if the confirmation of ARSI WS is prioritized. Conversely, if it is not confirmed there is a risk that second-line treatment will be delayed. This is a review of recent studies of ARSI WS. It also discusses future prospects in this field.

Characteristics of adverse drug reactions induced by flutamide and bicalutamide: a real-world pharmacovigilance study using FAERS

ABSTRACT Background Flutamide and bicalutamide are indicated for the management of prostate metastatic carcinoma. The current study evaluated the adverse drug reactions related to flutamide and bicalutamide in a real-world setting. Methods To quantify the signals of flutamide and bicalutamide associated adverse events (AEs), we used the US Food and Drug Administration Adverse Event Reporting System (FAERS) for this pharmacovigilance study using established pharmacovigilance methods. Results A total of 2711 AEs of flutamide were investigated as the primary suspected; 522 AEs were related to prostate cancer. A total of 4459 AEs were investigated as the primary suspected for bicalutamide; 2251 AEs were related to prostate cancer. The analysis demonstrated 29 signals for flutamide and 84 for bicalutamide. Liver function test was the most common AEs for flutamide, and malignant neoplasm progression was the most common for bicalutamide. The signal strength of Dementia Alzheimer’s type was 26.53 (17.89–39.35) and 26.33 (607.34), which had the highest strength for flutamide. Anti-androgen withdrawal syndrome exhibited the strongest signal for bicalutamide. Generating awareness of rare AEs that were not listed on the label is critical. Conclusions The analysis of the AE signals may provide support for prescribing flutamide and bicalutamide.

Impact of antiandrogen withdrawal syndrome in castration-resistant prostate cancer patients treated with abiraterone or enzalutamide.

To assess the impact of antiandrogen withdrawal syndrome after bicalutamide withdrawal in castration-resistant prostate cancer patients treated with androgen receptor-axis targeted agents. The study cohort comprised 94 patients treated with abiraterone (n=34) or enzalutamide (n=60) as a first-line androgen receptor-axis targeted agent for castration-resistant prostate cancer despite combined androgen blockade by castration with bicalutamide as the first-line therapy. The association between clinicopathological factors (including antiandrogen withdrawal syndrome) and therapeutic outcome after using abiraterone and enzalutamide was investigated. The decline in the prostate-specific antigen level after use of abiraterone or enzalutamide was comparable between patients with and without antiandrogen withdrawal syndrome. Antiandrogen withdrawal syndrome (hazard ratio 3.84, 95% confidence interval 1.29-11.45; P=0.016) was associated with a higher risk of progression on multivariate analysis, but not all-cause death after abiraterone use. Progression-free survival and overall survival after enzalutamide use did not differ between patients with and without antiandrogen withdrawal syndrome. The present data suggest a modest therapeutic efficacy of abiraterone in castration-resistant prostate cancer patients with anti-androgen withdrawal syndrome after bicalutamide withdrawal.

Prognostic and Predictive Factors for Anti-androgen Withdrawal in Castration-resistant Prostate Cancer.

We aimed to identify prognostic and predictive factors for anti-androgen withdrawal syndrome (AWS) to help guide decisions on anti-androgen withdrawal in castration-resistant prostate cancer (CRPC). This study included 95 patients with prostate cancer which progressed to CRPC despite primary androgen-deprivation therapy (ADT). AWS was defined as >50% prostate-specific antigen decline after anti-androgen withdrawal. Associations between AWS, and clinicopathological factors and prognosis were investigated. Among the 95 patients, 84 (88.4%) underwent anti-androgen withdrawal, among whom AWS was recognized in nine (10.8%). Gleason score and response duration to primary ADT were predictors of AWS. Long duration of response to primary ADT was also associated with better progression-free survival [hazard ratio (HR)=0.021, 95% confidence interval (CI)=0.0025-0.14, p<0.0001] and overall survival (HR=0.0042, 95% CI=0.0001-0.089, p<0.0001). Age (HR=7.19, 95% CI=1.08-54.27, p=0.041) and radiological/clinical progression (HR=3.14, 95% CI=1.35-6.43, p=0.010) were associated with worse overall survival. Intriguingly, radiological/clinical progression was associated with the differential effect of anti-androgen withdrawal on overall survival (interaction p=0.031). Patients who suffer radiological/clinical progression are unsuitable candidates for anti-androgen withdrawal.

Long-Lasting Antiandrogen Withdrawal Syndrome in Castration-Resistant Prostate Cancer: Three Cases With Complete Response

Long-Lasting Antiandrogen Withdrawal Syndrome in Castration-Resistant Prostate Cancer: Three Cases With Complete Response

Multicenter prospective study of switching from GnRH agonists to GnRH antagonist for patients with early stage of castration resistant prostate cancer as a second-line hormonal therapy.

183 Background: It was reported that GnRH antagonist could extend progression free survival for prostate cancer patients significantly longer than GnRH agonist in a first line hormonal therapy. However, the usefulness of switching from GnRH agonist to GnRH antagonist as a second hormonal therapy remains obscure. We performed a multicentral prospective study to investigate whether the switching from GnRH agonist to GnRH antagonist (degalerix) for patients with castration resistant prostate cancer (CRPC) as the 2nd line hormonal therapy was effective. Methods: 37 patients who were pathologically diagnosed as prostatic adenocarcinoma and developed CRPC after 1st line hormonal therapy with GnRH agonist plus anti-androgens were enrolled. After confirming anti-androgen withdrawal syndrome, they were treated with switching from GnRH agonists to degalerix. The primary endpoint was PSA response (PSA decline or up to 10% over baseline PSA). Secondary endpoints were the time to 25% PSA increase from the baseline (PSA response time), PSA progression free survival (PPFS), the time to treatment failure, cancer specific survival, radiographic PFS (rPFS), and safety. Results: Mean age was 76 years old, super high risk; 20 cases (54.1%), high risk; 11 cases (29.7%), intermediate risk; 5 cases (13.5%), low risk; one case (2.7%). PSA responder rate was 24.3% (9 cases). In responders, the median PSA response time was 5.75 months, the median PPFS was 1.77 months, and rPFS rate at 3 months was 96%. Regarding safety, only 2 cases (5.4%) showed G3 of AE. The PSA response had no relationship with the change of serum testosterone, LH nor FSH. Conclusions: The effectiveness of switching from GnRH agonist to GnRH antagonist showed to be limited. Although no predictive factor of the switching was recognized, some long-term responders were seen. We expect the possibility of switching to GnRH antagonist for patients in the early stage of CRPC, especially non-metastatic status. Clinical trial information: UNKNOWN.

Abiraterone acetate withdrawal syndrome: Speculations on the underlying mechanisms.

A 72-year-old man initially presented with lumbar and right chest pain, but was later found out to also have an elevated prostate-specific antigen (PSA) level at 2,000.0 ng/ml. Further evaluation disclosed metastatic prostate cancer involving the bones and lymph nodes. The patient was initially treated with combined androgen blockade (CAB) with leuprolide acetate and bicalutamide. After 6 months of CAB, the patient's PSA level began to rise from the nadir (85.1 ng/ml) to 113.3 ng/ml. Bicalutamide was withdrawn in anticipation of anti-androgen withdrawal syndrome and the PSA level declined temporally. However, it increased up to 517.0 ng/ml thereafter. Consequently, a year after CAB, abiraterone acetate (AA) was initiated at a standard dose of 1,000 mg daily in combination with 10 mg of prednisolone. PSA rapidly decreased to the nadir of 20.1 ng/ml thereafter. The PSA level remained stable until 2 years after AA administration. However, he decided to reduce the dose of AA to half of the standard dose (500 mg daily). Contrary to our expectations, the serum PSA level promptly decreased to a nadir of 8.1 ng/ml. Thereafter, the PSA level remained stable until 3 years and 9 months after AA administration. Subsequently, the patient stopped taking AA and prednisolone. However, to our surprise, the patient's serum PSA level decreased further to <1.0 ng/ml after AA discontinuation. His PSA remained <1.0 ng/ml without clinical or radiological progression for 1 year after AA withdrawal. Recently, it was reported that cessation of AA is associated with AA withdrawal syndrome in metastatic castration-resistant prostate cancer, defined as a PSA decrease after AA discontinuation, mimicking anti-androgen withdrawal syndrome. In the present study, explanations of the mechanisms underlying this phenomenon were explored, including mutant AR activation by alternative ligands.

Antiandrogen withdrawal syndrome (AAWS) in the treatment of patients with prostate cancer.

Antiandrogen withdrawal syndrome is an unpredictable event diagnosed in patients with hormone-sensitive prostate cancer treated with combined androgen blockade therapy. It is defined by prostate-specific antigen value reduction, occasionally associated with a radiological response, that occurs 4-6 weeks after first-generation antiandrogen therapy discontinuation. New-generation hormonal therapies, such as enzalutamide and abiraterone acetate, improved the overall survival in patients with metastatic castration-resistant prostate cancer, and recent trials have also shown the efficacy of abiraterone in hormone-sensitive disease. In the last few years, several case reports and retrospective studies suggested that the withdrawal syndrome may also occur with these new drugs. This review summarizes literature data and hypothesis about the biological rationale underlying the syndrome and its potential clinical relevance, focusing mainly on new-generation hormonal therapies. Several in vitro studies suggest that androgen receptor gain-of-function mutations are involved in this syndrome, shifting the antiandrogen activity from antagonist to agonist. Several different drug-specific point mutations have been reported. The association of the withdrawal syndrome for enzalutamide and abiraterone needs confirmation by additional investigations. However, new-generation hormonal therapies being increasingly used in all stages of disease, more patients may experience the syndrome when stopping the treatment at the time of disease progression, although the clinical relevance of this phenomenon in the management of metastatic castration-resistant prostate cancer remains to be defined.

Incidence and Characterization of Antiandrogen Withdrawal Syndrome After Discontinuation of Treatment With Enzalutamide in Castration-resistant Prostate Cancer.

Antiandrogen withdrawal syndrome (AAWS), manifested as a prostate-specific antigen (PSA) decline after discontinuation of a first-generation antiandrogen has been well characterized. The objective of the present study was to assess the incidence of AAWS with enzalutamide in men with metastatic castration-resistant prostate cancer. Patients from a single-institution cohort with metastatic castration-resistant prostate cancer who had discontinued enzalutamide after PSA or radiographic progression were included. AAWS after enzalutamide was defined as any PSA decline after discontinuation of enzalutamide. The baseline patient, disease, and treatment characteristics were compared between patients with and without AAWS after enzalutamide. Statistical analysis of the baseline characteristics included descriptive statistics using the Wilcoxon rank sum test and the Fisher exact test. The median duration of enzalutamide therapy was compared using the log-rank test, and the progression-free survival of the patients with AAWS was evaluated using the Kaplan-Meier method. Of 47 eligible patients, 5 experienced AAWS after enzalutamide discontinuation. The PSA response in these 5 patients was 84%, 32%, 17%, 15%, and 15%. The median AAWS response time until subsequent PSA progression was 3.3 months. No patient, disease, or treatment characteristics differed among the patients with and without AAWS after enzalutamide discontinuation. To the best of our knowledge, this is the largest reported cohort documenting the incidence and characterization of AAWS after enzalutamide to date. The AAWS frequency after enzalutamide was low and of short duration. No patient- or disease-related characteristics were associated with AAWS with enzalutamide. The occurrence of AAWS after enzalutamide was not clinically meaningful. Thus, accounting for this phenomenon in clinical practice or trial designs could be unnecessary.

Incidence and characterization of antiandrogen withdrawal syndrome (AAWS) after enzalutamide (ENZA) in patients (pts) with metastatic castration-refractory prostate cancer (mCRPC).

228 Background: AAWS manifested as PSA decline after discontinuation of first generation AAs, like bicalutamide, has been well characterized and reported. Objective of this study was to assess the incidence and characterize AAWS after ENZA in pts with mCRPC. Methods: From a single institution cohort, pts with mCRPC who discontinued ENZA after documented disease progression per PCWG2 criteria were included. AAWS after ENZA was defined as any degree of PSA decline after discontinuation of ENZA. Baseline pts, disease, and treatment characteristics were compared between Òpts with AAWS after ENZAÓ vs. Òpts without AAWS after ENZAÓ treated during the similar time period: median values were compared with the Wilcoxon rank sum test; proportions were compared with FisherÕs Exact test; and the log rank test was used to compare PFS (Table). Results: 5 pts of 72 eligible pts (~7%) experienced AAWS after discontinuation of ENZA. The levels of PSA decline were as follows: 84%, 32%, 17%, 15% and 15%, respectively. Median AAWS response time, until subsequent PSA progression, was 6 weeks. None of the pts, disease or treatment characteristics (such as prior duration of response to ENZA) were different among Òpts with AAWS after ENZAÓ vs. Òpts without AAWS after ENZAÓ. Conclusions: This is the largest study reporting on the incidence and characterization of AAWS after ENZA. AAWS after ENZA is infrequent (~7%), of short duration (6 weeks), and not predicted by pts, disease or treatment related characteristics. Unlike AAWS after first generation AR inhibitors, like bicalutamide, the AAWS after ENZA is not clinically meaningful and should not have any bearing on the eligibility criteria of clinical trials conducted in the post ENZA setting. [Table: see text]

Long-term complete response of antiandrogen withdrawal syndrome in a patient with metastatic prostate cancer: A case report

Antiandrogen withdrawal syndrome (AWS) is a well-established phenomenon in prostate cancer treated with combined androgen blockade (CAB). AWS is generally defined as subjective and/or objective improvement following discontinuation of an antiandrogen. However, the duration of the AWS response is usually limited. In addition, a complete response is quite rare. We herein present the case of a patient who achieved complete response from AWS, with the duration of this response lasting for >6 years. A 72-year-old man with metastatic prostate cancer received CAB with a luteinizing hormone-releasing hormone analog and bicalutamide. In addition, for local cancer control, external beam radiation therapy (70 Gy) to the prostate was performed. Subsequently, the serum prostate-specific antigen (PSA) level reached a nadir (undetectable level). Four years later, the patient's serum PSA level started to rise, and bicalutamide was discontinued to confirm AWS at a serum PSA level of 0.34 ng/ml. The PSA level immediately decreased again to an undetectable level (0.00 ng/ml), where it has been remained for 6 years. Bone scintigraphy and computed tomography scans have shown no evidence of bone or other metastases since the introduction of AWS. To the best of our knowledge, there have been no reports of such a long duration of complete response from AWS. Therefore, this phenomenon should always be considered, even in patients with advanced disease.

Does abiraterone withdrawal syndrome (AWS) exist also in metastatic castration-resistant prostate cancer (mCRPC) first-line setting?

344 Background: AWS is a recently phenomenon observed in mCRPC patients (pts) characterized by a PSA reduction with or without objective response after abiraterone acetate (AA) discontinuation. This syndrome has clinical features similar to antiandrogen withdrawal syndrome and was described in pts who treated with AA in the post-docetaxel setting. At the best of our knowledge, to date AWS was never described in chemo-naïve mCRPC pts. Methods: We retrospectively reviewed clinical records of mCRPC pts treated with first-line AA at our Institution. All pts were treated with AA 1,000 mg + prednisone (PDN) 10 mg po daily; the treatment was continued until progression disease (PD) which required an imaging confirmation too. After PD, we also discontinued the PDN administration. For each pt we recorded pre and post-AA clinical history, treatment details and outcomes. AWS was defined by PSA reduction ≥ 25% compared to the AA-end values observed in the first month after AA stop. Results: From September 2014, eight pts received first-line AA and, to date, 6 patients (75%) who discontinued the treatment due to PD are evaluable for AWS occurrence. We observed an AWS in 2/6 (33.3%). The first patient, a 76 year-old man, who experienced a PD after 12 wks AA treatment, had a 69% reduction in PSA with PSA dropping from 60 ng/mL to 19.47 ng/mL after about 30 days from the discontinuation. The second patient, 83 years old, treated with AA for 12 weeks, had a reduction in PSA from 112.2 ng/mL to 55 ng/mL at one-month (51% reduction) and to 35.36 ng/mL at two months (68.5% reduction) after AA and PDN discontinuation; after 9 wks the AWS is still ongoing. Conclusions: Notwithstanding the limits of the small sample size, our data shows for the first time that AWS can be observed also in mCRPC patients receiving AA as first-line treatment. Larger observations are needed to establish frequency and clinical role of this phenomenon. Although pathogenetic mechanisms and predictive factors are still unclear, AWS may represent a possibility to delay the second line start for mCRPC pts.

Identification of a predictive factor of metastatic castration-resistant prostate cancer patients’ response to alternative antiandrogen therapy with flutamide.

321 Background: Recently, new androgen pathway inhibitors, abiraterone and enzalutamide, are demonstrated to improve overall survival for metastatic castration-resistant prostate cancer (mCRPC). In Japan, alternative antiandrogen (AA) as second-line hormonal therapy for mCRPC that relapses after initial hormone therapy have been commonly used before new androgen pathway inhibitors. In this study, we attempted to identify the predictive factors for efficacy of AA as second-line hormone therapy. Methods: We identified consecutive 65 mCRPC patients treated with AA as second-line hormonal therapy. All patients were treated with maximum androgen blockade (MAB) initially and evaluated antiandrogen withdrawal syndrome after relapse. We analyzed the correlations between progression-free survival (PFS) of AA and clinicopathological characteristics, including patients’ age, initial PSA levels, PSA levels at flutamide induction, Gleason scores, T stage, N stage, extent of disease (EOD) classifications on bone scan, and the previous duration of prostate cancer sensitivity to MAB. Results: The median duration of prostate cancer sensitivity to MAB was 11.3 months (range: 1.5-53.0 months). In multivariate analysis, four significant risk factors for poor PFS were identified; initial PSA levels ( &gt; 263 ng/mL vs ≤ 263; HR 0.53, p = 0.038), N stage (1 vs 0; HR 3.00, p = 0.001), EOD classifications (3-4 vs 1-2; HR 2.50, p = 0.007), and the previous duration of prostate cancer sensitivity to MAB ( &lt; 12 months vs ≥ 12; HR 2.16, p = 0.026). We stratified the patients into two cohorts with low risk (0-2 risk factor present) and high risk (3-4 risk factors present). We found a significant difference in PFS among risk groups (median PFS 7.3 months vs 1.5, p &lt; 0.000). Conclusions: Initial PSA, N stage, EOD classifications on bone scan, and the previous duration of prostate cancer sensitivity to MAB were the significant predictive factors for efficacy of AA as second-line hormone therapy in patients with mCRPC. These findings might support that decision-making of when to start the new AR pathway inhibitors.

Switching and withdrawing hormonal agents for castration-resistant prostate cancer.

The antiandrogen withdrawal syndrome (AAWS) is characterized by tumour regression and a decline in serum PSA on discontinuation of antiandrogen therapy in patients with prostate cancer. This phenomenon has been best described with the withdrawal of the nonsteroidal antiandrogens, bicalutamide and flutamide, but has also been reported with a wide range of hormonal agents. Mutations that occur in advanced prostate cancer and induce partial activation of the androgen receptor (AR) by hormonal agents have been suggested as the main causal mechanism of the AAWS. Corticosteroids, used singly or in conjunction with abiraterone, docetaxel and cabazitaxel might also be associated with the AAWS. The discovery of the Phe876Leu mutation in the AR, which is activated by enzalutamide, raises the possibility of withdrawal responses to novel hormonal agents. This Review focusses on the molecular mechanisms responsible for withdrawal responses, the role of AR mutations in the development of treatment resistance, and the evidence for the sequential use of antiandrogens in prostate cancer therapy. The implications of AR mutations for the development of novel drugs that target the AR are discussed, as are the challenges associated with redefining the utility of older treatments in the current therapeutic landscape.

Complete response to ethnylestradiol prolonged for almost two years in patients with castration-resistant prostate cancer

An 80-year-old man with an elevated prostate-specific antigen (PSA) level of 120 ng/mL) presented to the hospital in February 2011. A prostate needle biopsy was performed, and pathological examination revealed prostatic adenocarcinoma. The Gleason score was 4+5=9. Computed tomography revealed metastases of the pelvic lymph nodes. Combined androgen blockade was started. The PSA concentration decreased to 1.68 ng/mL, but started increasing again in August 2012 to 6.08 ng/mL. Although bicalutamide was discontinued due to antiandrogen withdrawal syndrome, the PSA concentration increased even more. The PSA concentration reached 21.62 ng/mL in September 2012, at which time ethnylestradiol was started. The PSA concentration decreased again and has remained below the limit of sensitivity for almost 2 years. To our knowledge, this is first case report describing a complete response to ethnylestradiol that lasted for almost 2 years in a patient with castration-resistant prostate cancer.

Is there an antiandrogen withdrawal syndrome with enzalutamide?

To examine prostate-specific antigen (PSA) levels after enzalutamide discontinuation to assess whether an antiandrogen withdrawal syndrome (AAWS) exists with enzalutamide. We retrospectively identified 30 consecutive patients with metastatic prostate cancer who were treated with enzalutamide after docetaxel. Post-discontinuation PSA results were available for all patients and were determined at 2-weekly intervals until starting further anticancer systemic therapy. PSA withdrawal response was defined as a PSA decline by ≥50% from the last on-treatment PSA, with a confirmed decrease ≥3 weeks later. Patient characteristics were evaluated in relation to the AAWS using univariate logistic regression analysis. The median (range) patient age was 70.5 (56-86) years and the median (range) follow-up was 9.0 (0.5-16) months. The most common metastatic sites were the bone (86.7%) and lymph nodes (66.7%). Most patients (70%) had previously received abiraterone and 12 patients (40%) had also received cabazitaxel. The median (range) treatment duration with enzalutamide was 3.68 (1.12-21.39) months. PSA levels after enzalutamide withdrawal were monitored for a median (range) time of 35 (10-120) days. Only one patient (3.3%) had a confirmed PSA response ≥50% after enzalutamide discontinuation. One patient (3.3%) had a confirmed PSA response of between 30 and 50% and another patient (3.3%) had an unconfirmed PSA response of between 30 and 50%. The median overall survival was 15.5 months (95% CI 8.1-24.7). None of the factors analysed in the univariate analysis were significant predictors of PSA decline after enzalutamide discontinuation. This retrospective study provides the first evidence that enzalutamide may have an AAWS in a minority of patients with metastatic castration-resistant prostate cancer. Further studies are needed to confirm the existence of an enzalutamide AAWS and to assess its relevance in prostate cancer management.

Androgen Receptor Antagonists in the Treatment of Prostate Cancer

Antiandrogens that block androgen action through the androgen receptor, often in conjunction with chemical or surgical castration, have been widely used for the treatment of advanced prostate cancer. Although this treatment produces a significant clinical response in most of the patients, the majority of the responders eventually develop recurrences termed castration-resistant prostate cancer. In addition, clinically available androgen receptor antagonists have been shown to possess agonist activity, resulting in an increase in serum prostate-specific antigen levels, which is known as the antiandrogen withdrawal syndrome. Recent studies have demonstrated that new types of androgen receptor signaling inhibitors improve survival in men with castration-resistant prostate cancer. Moreover, other drugs may have the potential of not inducing androgen withdrawal response. This article reviews the characteristics of classical and recent androgen receptor antagonists as well as their clinical efficacy in prostate cancer patients. Novel experimental compounds that may more specifically and effectively target androgens and/or androgen receptor signals in hormone-naive and possibly castration- resistant prostate cancer cells are also discussed. Keywords: Androgen, androgen receptor, antiandrogen, castration, combined androgen blockade, cytochrome P450-17, hormonal therapy, prostate cancer.

Prostate cancer: an enzalutamide antiandrogen withdrawal syndrome.

Prostate cancer: an enzalutamide antiandrogen withdrawal syndrome.

Enzalutamide activity in patients with metastatic castration resistant prostate cancer (mCRPC) previously responding to antiandrogen withdrawal syndrome (AWS): A preliminary report.

e16058 Background: AWS is defined as decline in PSA after withdrawal of an antiandrogen (AA) during maximum androgen blockade and it has been described in less than 20% of mCRPC patients. The most ...

Is there an anti-androgen withdrawal syndrome for enzalutamide?

The anti-androgen withdrawal syndrome (AAWS) can be seen in one-third of patients after discontinuation of first-generation non-steroidal anti-androgen therapy. With the introduction of new agents for anti-androgen therapy as well as alternate mechanisms of action, new therapeutic options before and after docetaxel chemotherapy have arisen (Ohlmann et al. in World J Urol 30(4):495-503, 2012). The question regarding the occurrence of an enzalutamide withdrawal syndrome (EWS) has not been evaluated yet. In this study, we assess prostate-specific antigen (PSA) response after discontinuation of enzalutamide. In total 31 patients with metastatic castration-resistant prostate cancer (mCRPC) underwent an enzalutamide withdrawal and were evaluated. Data were gathered from 6 centres in Germany. Patients with continuous oral administration of enzalutamide with rising serum PSA levels were evaluated, starting from enzalutamide withdrawal until subsequent therapy was initiated, follow-up ended or death of the patient occurred. Statistical evaluation was performed applying one-sided binomial testing using R-statistical software, version 3.0.1. Mean withdrawal follow-up was 6.5 weeks (range 1-26.1 weeks). None of the 31 patients showed a PSA decline. Mean relative PSA rise over all patients was 73.9 % (range 0.5-440.7 %) with a median of 44.9 %. If existent, an AAWS is at least very rare for enzalutamide in patients with mCRPC after taxane-based chemotherapy and does not play a clinical role in this setting. This may be attributed to the different pharmacodynamics of enzalutamide. Longer duration of therapy or a longer withdrawal interval may reveal a rare EWS in the future.