Primary Merkel Cell Carcinoma Research Articles

Exploring the effects of Merkel cell polyomavirus T antigens expression in REH and MCC13 cells by methylome and transcriptome profiling.

Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer with a tripled incidence in the US and Europe over the past decade. Around 80% of MCC is linked to Merkel cell polyomavirus, but the cell of origin remains unknown. We stably introduced Merkel cell polyomavirus (MCPyV)-sT) and LT antigens to MCC13 and REH cell lines, analyzing DNA methylation and gene transcriptional regulation. Gene ontology analysis assessed MCPyV effects, and integrative analysis correlated gene expression and methylation. Expression patterns were compared with 15 previously sequenced primary MCCs. We found that MCPyV-LT induces DNA methylation changes in both cell lines, while MCPyV-sT only affected REH cells. Greater gene expression changes are observed in MCC13 cells, with upregulated genes associated with cellular components and downregulated genes related to biological processes. Integrative analysis of differentially expressed genes (DEG) and differentially methylated regions (DMR) of REH cell lines revealed that no genes were commonly methylated and differentially expressed. The study compared DEGs and DMG in MCC13 and REH cells to overlapping genes in MCPyV-positive cell lines (MKL1, MKL2, and WaGa), identifying hypomethylated genes in the gene body and hypermethylated genes at TSS1500. GO analysis of the two cell lines showed that MCPyV-TAs can downregulate genes in MHC-I pathways; this downregulation offers a target that can be used to create novel and efficient MCC immunotherapy approaches. Finally, it was confirmed that MCPyV-LT controls gene expression in MCC tissues using an integrative investigation of DNA methylation and gene expression.

EE413 Predictive and Interpretable Machine Learning of Economic Burden: The Role of Chronic Conditions Among Patients with Incident Primary Merkel Cell Carcinoma

EE413 Predictive and Interpretable Machine Learning of Economic Burden: The Role of Chronic Conditions Among Patients with Incident Primary Merkel Cell Carcinoma

Different prognosis in cutaneous early-onset and late-onset Merkel cell carcinoma: a population-based retrospective study.

Merkel cell carcinoma (MCC) is a rare and highly aggressive form of skin cancer. However, there is limited research on the clinicopathological features of early-onset MCC (EOMCC) and the differences between EOMCC and late-onset MCC (LOMCC). Our objective was to evaluate the clinicopathological features and cancer-specific survival (CSS) of EOMCC. Our cohort study analyzed data from the Surveillance, Epidemiology, and End Results (SEER) database from January 1, 2018, to December 31, 2020. Data from 1941 patients who were diagnosed with primary cutaneous MCC were included. We then divided the patients with MCC into two groups: those with EOMCC (526 patients) and those with LOMCC (1415 patients). CSS is used as the primary outcome. The EOMCC group exhibited trends toward advanced tumor progression, an expanded surgical scope, increased lymph node retrieval, intensified radiotherapy, greater utilization of systemic therapy, and a better prognosis. Multivariate analysis revealed that LOMCC (HR 3.305 [2.002-5.456], P < 0.001), advanced T stage (HR 1.430 [1.139-1.797], P = 0.002), advanced N stage (HR 1.522 [1.221-1.897], P < 0.001), M1 stage (HR 2.587 [1.480-4.521], P < 0.001), and radiation (HR 0.586 [0.410-0.837], P = 0.003) were significantly associated with CSS. Among these factors, EOMCC/LOMCC was most strongly associated with CSS, indicating that LOMCC is an independent risk factor for CSS. Interestingly, we found that regional EOMCC and localized or in situ LOMCC had almost completely overlapping survival curves (Plog-rank = 0.620). Additionally, we observed that the TNM staging + age model was a more accurate predictor of CSS among MCC patients than using TNM staging alone. We found that EOMCC has distinct clinicopathological features compared to LOMCC. EOMCC is associated with better CSS. The combination of TNM staging and age was more accurate for predicting patient outcomes than TNM staging alone.

Color Analysis of Merkel Cell Carcinoma: A Comparative Study with Cherry Angiomas, Hemangiomas, Basal Cell Carcinomas, and Squamous Cell Carcinomas.

Merkel cell carcinoma (MCC) is recognized as one of the most malignant skin tumors. Its rarity might explain the limited exploration of digital color studies in this area. The objective of this study was to delineate color alterations in MCCs compared to benign lesions resembling MCC, such as cherry angiomas and hemangiomas, along with other non-melanoma skin cancer lesions like basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), utilizing computer-aided digital color analysis. This was a retrospective study where clinical images of the color of the lesion and adjacent normal skin from 11 patients with primary MCC, 11 patients with cherry angiomas, 12 patients with hemangiomas, and 12 patients with BCC/SCC (totaling 46 patients) were analyzed using the RGB (red, green, and blue) and the CIE Lab color system. The Lab color system aided in estimating the Individual Typology Angle (ITA) change in the skin, and these results are documented in this study. It was demonstrated that the estimation of color components can assist in the differential diagnosis of these types of lesions because there were significant differences in color parameters between MCC and other categories of skin lesions such as hemangiomas, common skin carcinomas, and cherry hemangiomas. Significant differences in values were observed in the blue color of RGB (p = 0.003) and the b* parameter of Lab color (p < 0.0001) of MCC versus cherry angiomas. Similarly, the mean a* value of Merkel cell carcinoma (MCC) compared to basal cell carcinoma and squamous cell carcinoma showed a statistically significant difference (p < 0.0001). Larger prospective studies are warranted to further validate the clinical application of these findings.

Primary tumor site for localized Merkel cell carcinoma drives different management strategies without impacting oncologic outcomes

Background and purposeClinically localized Merkel cell carcinoma (MCC) has been associated with high rates of disease relapse. This study examines how primary tumor anatomic site drives patterns of care and outcomes in a large cohort treated in the contemporary era. Materials and methodsPatterns of care and associated outcomes were evaluated for clinically Stage I-II MCC patients treated at our institution with adjuvant radiation therapy (RT) to the primary site and/or regional nodal basin as a component of their curative intent therapy between 2014–2021. ResultsOf 80 patients who met inclusion criteria, the primary tumor anatomic site was head and neck (HN) for 42 (53%) and non-head and neck (NHN) for 38 (47%). Primary tumor risk factors were similar between cohorts. Fewer patients with HN tumors had wide local excision (WLE; HN-81% vs. NHN-100% p < 0.01). Of those undergoing WLE, patients with HN tumors received higher dose adjuvant RT (>50 Gy: HN-70% vs. NHN-8%; p < 0.01). Patients with HN tumors were less likely to undergo sentinel lymph node biopsy (HN-62%vs. NHN-100%; p < 0.01) and more likely to have elective nodal RT (HN-48% vs. NHN-0%). Despite varying management strategies, there was no significant difference in local recurrence-free survival (3-yr LRFS HN-94% vs. NHN-94%; p = 0.97), nodal recurrence-free survival (3-yr NRFS HN-89% vs. NHN-85%; p = 0.71) or overall recurrence-free survival (3-yr RFS 73% HN vs. 80% NHN; p = 0.44). ConclusionsAmong patients with primary MCC who had RT as a component of their initial treatment strategy, anatomically-driven heterogeneous treatment approaches were associated with equally excellent locoregional disease control.

Primary Merkel cell carcinoma is associated with increased, extended risk of subsequent melanoma and nonepithelial skin cancer

Primary Merkel cell carcinoma is associated with increased, extended risk of subsequent melanoma and nonepithelial skin cancer

Single-cell dissection of Merkel cell carcinoma heterogeneity unveils transcriptomic plasticity and therapeutic vulnerabilities

Merkel cell carcinoma (MCC), a rare but aggressive skin cancer, remains a challenge in the era of precision medicine. Immune checkpoint inhibitors (ICIs), the only approved therapy for advanced MCC, are impeded by high primary and acquired resistance. Hence, we dissect transcriptomic heterogeneity at single-cell resolution in a panel of patient tumors, revealing phenotypic plasticity in a subset of treatment-naive MCC. The tumor cells in a "mesenchymal-like" state are endowed with an inflamed phenotype that portends a better ICI response. This observation is also validated in the largest whole transcriptomic dataset available from MCC patient tumors. In contrast, ICI-resistant tumors predominantly express neuroepithelial markers in a well-differentiated state with "immune-cold" landscape. Importantly, a subtle shift to "mesenchymal-like" state reverts copanlisib resistance in primary MCC cells, highlighting potential strategies in patient stratification for therapeutics to harness tumor cell plasticity, augment treatment efficacy, and avert resistance.

Expression of Genes Associated With Epithelial-Mesenchymal Transition in Merkel Cell Polyomavirus–Negative Merkel Cell Carcinoma

Two accepted possible pathways for Merkel cell carcinoma (MCC) pathogenesis include the clonal integration of the Merkel cell polyomavirus (MCPyV) into the neoplastic cells and by UV irradiation. We hypothesize that, in UV etiology, the expression of genes associated with epithelial-mesenchymal transition (EMT) would be higher in MCPyV-negative MCCs. We compared RNA expression in 16 MCPyV-negative with that in 14 MCPyV-positive MCCs in 30 patients using NanoString panel of 760 gene targets as an exploratory method. Subsequently, we confirmed the findings with a publicly available RNA sequencing data set. The NanoString method showed that 29 of 760 genes exhibited significant deregulation. Ten genes (CD44, COL6A3, COL11A1, CXCL8, INHBA, MMP1, NID2, SPP1, THBS1, and THY1) were part of the EMT pathway. The expression of CDH1/E-cadherin, a key EMT gene, and TWIST1, regulator gene of EMT, was higher in MCPyV-negative tumors. To further investigate the expression of EMT genes in MCPyV-negative MCCs, we analyzed publicly available RNA sequencing data of 111 primary MCCs. Differential expression and gene set enrichment analysis of 35 MCPyV-negative versus 76 MCPyV-positive MCCs demonstrated significantly higher expression of EMT-related genes and associated pathways such as Notch signaling, TGF-β signaling, and Hedgehog signaling, and UV response pathway in MCPyV-negative MCCs. The significance of the EMT pathway in MCPyV-negative MCCs was confirmed independently by a coexpression module analysis. One of the modules (M3) was specifically activated in MCPyV-negative MCCs and showed significant enrichment for genes involved in EMT. A network analysis of module M3 revealed that CDH1/E-cadherin was among the most connected genes (hubs). E-cadherin and LEF1 immunostains demonstrated significantly more frequent expression in MCPvV-negative versus MCPyV-positive tumors (P < .0001). In summary, our study showed that the expression of EMT-associated genes is higher in MCPyV-negative MCC. Because EMT-related proteins can be targeted, the identification of EMT pathways in MCPyV-negative MCCs is of potential therapeutic relevance.

Primary Nodal Merkel Cell Carcinoma: Rare Presentation

Merkel cell carcinoma (MCC) is a very rare high-grade neuroendocrine carcinoma that is frequently located in the skin. Although most cases are associated with Merkel cell polyomavirus, there are also cases in which the virus cannot be detected. The purpose of presenting the case of MCC with primary nodal involvement is due to its rare presentation. &#x0D; A 59-year-old male patient presented to the hospital with painless mass in the neck. Imaging analyses revealed necrotic lymphadenopathies on the neck, measuring up to 4.5 cm in size. After an explorative surgery with preliminary diagnoses of lymphoma and squamous cell carcinoma , samples taken from the excised mass showed high-grade neuroendocrine carcinoma morphology. In addition to neuroendocrine markers, CK7 and CK20 positivity were observed in the immunohistochemical tests performed. As a result, the case was evaluated in favor of MCC with negativity of markers performed to exclude other malignancies. Subsequently, a diagnosis of primary nodal MCC was made due to the absence of a different focus other than lymph node on PET imaging analysis.&#x0D; The differential diagnosis should be kept broad due to the histopathological morphology of small round cell malignant tumors. In addition in high-grade neuroendocrine carcinomas, the possibility of MCC should be ruled out especially if CK20 positivity is present. Although is has been reported that primary nodal MCC cases have a better clinical course compared to nodal metastatic cases with a known primary, there are limited case series studies on this topic. A multisystem approach is recommended for proper clinical management.

No difference in survival for primary cutaneous Merkel cell carcinoma after Mohs micrographic surgery and wide local excision

The preferred treatment for clinically node-negative Merkel cell carcinoma (MCC) is surgical excision in conjunction with sentinel lymph node biopsy. There is limited large-scale research on survival outcomes by surgical approach for management of the primary tumor. To compare overall and MCC-specific survival outcomes in clinically and pathologically node-negative MCC patients treated with wide-local excision (WLE) and Mohs micrographic surgery (MMS) in a nationally representative sample. Overall and MCC-specific survival outcomes for primary MCC tumors contained in the SEER-18 database from 1989 to 2015 were stratified by surgical modality and analyzed via competing risk analysis. A total of 2,359 US adults with MCC were included in the analysis. For overall and MCC-specific survival, there was no significant difference in survival outcomes between WLE and MMS on multivariable analysis ((HR 1.04 [95% CI 0.88 - 1.22]; SHR 0.76 [95% CI 0.53 - 1.09]). Sentinel lymph node biopsy (SLNB) was associated with improved overall survival and MCC-specific survival. Retrospective design of SEER and the lack of covariates such as comorbidities and immunostaining. There is no survival disadvantage for MMS compared to WLE as the surgical modality for primary cutaneous MCC. SLNB should be coordinated prior to MMS.

Defining the Profile of Patients with Primary Merkel Cell Carcinoma in Central Italy: A Retrospective Analysis.

Simple SummaryMerkel cell carcinoma is rarely suspected and often misdiagnosed in the clinical setting. Robust epidemiological data are missing, contributing to a lack of knowledge of this type of tumor among clinicians. We aimed to demographically and clinically characterize Merkel cell carcinoma patients and the tumor’s features through a multicenter real-world analysis of patients from Central Italy from 2015 to 2020. Our study revealed a higher incidence rate compared to the one estimated for the Italian population, with the lower limbs as the anatomical site affected the most. We also report that several specialists are involved in the first-line management of the pathology. In this light, a deeper knowledge of this tumor is advised.Merkel cell carcinoma (MCC) is a rare neuroendocrine skin cancer that usually occurs in elderly people on sun-exposed areas, with a predisposition to local recurrence. Evidence suggests a growing incidence over the past decade; however, robust epidemiologic data are still lacking. We describe the MCC population in clinical practice in a retrospective analysis of demographic, clinical, and tumor characteristics from medical records of primary MCC patients, between 2015 and 2020, at six dermatology clinics in Central Italy. Ninety-four patients were included (57.4% male; mean age 78.2 ± 10.1 years, range 47–99 years). The estimated incidence rate of MCC was 0.93 per 100,000 inhabitants/year. Lower limbs were the most frequently affected site (31.5%), and 54% of patients for whom information was available were immunosuppressed. Lymph node involvement was reported in 42.5% of patients, and distant metastases in almost 20%. Most patients underwent surgery for tumor excision and were mainly referred to specialized dermatology clinics by dermatologists (47.9%) and general surgeons (28.7%). Apart from the relatively balanced prevalence of MCC in men and women, the predominant location on lower limbs, and the higher incidence rate compared with previous reports in Italy, this population is, overall, similar to the populations described in other observational studies. MCC management requires the involvement of several specialties. Increased awareness of MCC and standardization of its management are urgently needed.

S3551 Gastric Metastasis of Merkel Cell Carcinoma: A Rare Cancer

Introduction: Merkel Cell Carcinoma (MCC) is a rare aggressive cutaneous neuroendocrine carcinoma. MCC is localized in 65% of cases, 26% cases spread to lymph nodes and metastasis is seen in 8% of cases. Stomach metastasis is rare site of metastasis, seen in 0.2 to 0.7% of cases on autopsy. CK 20 is a sensitive and specific marker of MCC. We present a case of a 63-year-old man who presented with chronic anemia and was found to have gastric metastasis of his cutaneous Merkel Cell Carcinoma. Case Description/Methods: A 63-year Caucasian man with pertinent history for hypertension, chronic anemia on iron therapy and stage IV neuroendocrine cutaneous tumor of left thigh with distant metastasis on treatment presented with melena, worsening fatigue, and shortness of breath for 2 weeks. Two months prior to this hospitalization, the patient was admitted for symptomatic anemia where patient had undergone Upper Gastrointestinal (UGI) Endoscopy. It had revealed non-bleeding gastric ulcers with pigmented material and biopsy was negative for malignancy (Figure a). On presentation his labs were significant for hemoglobin/hematocrit of 5.2/14.7% (g/dL/%). Computed Tomography Angiogram of abdomen and pelvis revealed a GI bleeding source within the proximal stomach. UGI endoscopy was performed after adequate resuscitation which revealed a large, fungating, infiltrative and ulcerated masses in the body of the stomach (Figure b). Biopsies showed malignant cells with immunohistochemical staining positive for chromogranin, synaptophysin, CK7, and CK20. It was reported that the immunomorphological features of initial biopsy of left posterior thigh were like this gastric biopsy. It was concluded that the patient's gastric mass was metastatic MCC. Discussion: MCC is a rare extremely aggressive carcinoma. Its spread to stomach is rare but should be considered in patients with cutaneous neuroendocrine tumor who present with iron deficiency anemia/GI bleeding. In addition, gastric metastasis is exponentially aggressive. Our patient’s gastric ulcer with negative biopsy grew into a fungating mass with proven MCC in two months. Thus, we would also like to highlight the importance of re-biopsy when the index of suspicion is high. Our patient’s initial biopsies were negative for malignancy while subsequent biopsies showed MCC. A combination surgical excision and loco-regional radiotherapy is used for treatment of aggressive primary MCC without distant metastasis. Radiotherapy, or combination with chemotherapy can be used for unresectable MCC.Figure 1.: (a) Initial UGI endoscopy done 2 months before the presentation. Shown above is gastric ulcer with pigmentation in Gastric body and Fundus (b) A large, fungating, infiltrative and ulcerated mass with no bleeding at gastric body. Biopsy of this mass showed MCC.

Mohs micrographic surgery reduces the need for a repeat surgery for primary Merkel cell carcinoma when compared to wide local excision: A retrospective cohort study of a commercial insurance claims database

To the Editor: Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine tumor with high rates of local recurrence and distant metastasis. Although wide local excision (WLE) is the standard of care for primary MCC, Mohs micrographic surgery (MMS) is often used for cases requiring tissue preservation, with multiple retrospective studies demonstrating comparable outcomes with respect to margin status, overall survival, and MCC-specific death.1 Here, we aimed to examine whether surgical modality for primary early-stage MCC correlates with the utilization pattern of subsequent interventions, such as sentinel lymph node biopsy (SLNB), adjuvant therapies, and additional surgeries.

Dataset for the Reporting of Merkel Cell Carcinoma: Recommendations From the International Collaboration on Cancer Reporting (ICCR).

Accurate and complete pathology reports are critical for the optimal management of cancer patients. Protocols for the pathologic reporting of Merkel cell carcinoma (MCC) have been developed independently by the Royal College of Pathologists (UK) and the College of American Pathologists. In this study, data elements for pathologic reporting of MCC were analyzed by an international panel of pathologists and clinicians with the aim of developing a common, internationally agreed upon dataset useful for clinical practice. The International Collaboration on Cancer Reporting expert review panel developed a protocol containing "core" (required) and "noncore" (recommended) elements. Core elements were defined as those that had evidentiary support and were unanimously agreed upon by the review panel as essential for the clinical management, staging, and/or assessment of prognosis in patients with MCC. Noncore elements were those considered to be clinical of interest, but with lesser degrees of supportive evidence or nonactionable implications. Ten core data elements for pathology reports on primary MCC were defined. Development and agreement on this evidence-based protocol at an international level was accomplished in a timely and efficient manner. The template developed for melanoma reporting was used as a structural base for this initiative. It is applicable to, and may facilitate the development of, protocols for other tumor types. Widespread utilization of an internationally agreed upon structured pathology dataset for MCC can be expected to lead to improved patient management. It should also facilitate collaborative clinical research.

Sentinel lymph node biopsy in Merkel cell carcinoma: Rates and predictors of compliance with the National Comprehensive Cancer Network guidelines

To the Editor: Primary Merkel cell carcinoma (MCC) has a 25% to 30% risk of occult nodal metastasis,1 and the National Comprehensive Cancer Network (NCCN) guidelines recommend sentinel lymph node biopsy (SLNB) in all patients without clinical nodal disease or known metastasis.2 SLNB status guides the prognosis and indications for adjuvant therapy.1 The rates of SLNB compliance have not been studied for MCC.

Merkel cell carcinoma on the dorsalis pedis with both dot‐like perinuclear and cytoplasmic patterns of CK20 positivity

Classically known to be a tumor of the head and neck region, primary Merkel cell carcinoma (MCC) has rarely been reported in the lower leg. The present case showed both dot‐like perinuclear and cytoplasmic patterns of CK20 positivity in the primary MCC. We propose that the presence of both dot‐like perinuclear and cytoplasmic patterns of CK20 could reflect the diversity of MCC origin from stem cell to mature Merkel cells in our patient.

Vulvar neuroendocrine carcinoma that is independent of merkel cell polyomavirus and human papillomavirus suggests endometrial cancer recurrence: a case report

BackgroundVulvar neuroendocrine carcinomas with small cell morphology need an appropriate differential diagnosis with respect to primary Merkel cell carcinomas, primary small cell neuroendocrine carcinomas, and secondary/metastatic carcinomas. Herein, we report a woman with a history of endometrial carcinoma led to neuroendocrine vulvar carcinoma.Case presentationAn 82-y-old woman with right vulvar swelling was transferred to our hospital. Computed tomography scan showed a 75 mm irregular mass in her right vulva. Three years ago, she had been diagnosed with endometrial endometrioid carcinoma stage IA and had undergone surgery. Vulvar biopsy revealed neuroendocrine carcinomas with small cell morphology. Immunohistochemical staining showed that the vulvar tumor was positive for CD56 and chromogranin A, but negative for Merkel cell polyomavirus and cytokeratin 20. Incidentally, her endometrial carcinoma was also positive for CD56 and chromogranin A. Human papillomavirus DNA typing analysis of vulvar tumor was negative. Hence, the vulvar tumor seemed to be a recurrence of the endometrial cancer rather than a primary vulvar neuroendocrine carcinoma. The patient died of the disease within a month.ConclusionWe report a case of vulvar neuroendocrine carcinoma that is independent of Merkel cell polyomavirus and human papillomavirus, thereby suggesting a recurrence of endometrial cancer. Immunohistochemical and virological analyses helped in the differential diagnosis of the neuroendocrine carcinoma.

Evaluation of clinical characteristics and pre-biopsy impressions of primary Merkel cell carcinoma of the skin.

Merkel cell carcinoma is an aggressive carcinoma of the skin notable for protean presentation on physical exam. A retrospective cohort of 232 patients with primary cutaneous Merkel cell carcinoma was reviewed for availability of data on pre-biopsy clinical differential diagnosis based on clinical exam. Data was available for 192 patients (83%). The three most common impressions were cyst (33.3%), basal cell carcinoma (31.8%), and squamous cell carcinoma (19.8%). Merkel cell carcinoma was correctly suspected in only 13 cases (6.8%). A greater proportion of lesions that were less than or equal to 2 cm in diameter (10.2%) or carried BCC as a co-diagnosis (11.5%) were correctly suspected as Merkel cell carcinoma prior to biopsy, versus lesions greater than 2 cm in diameter (1.6%) or carrying SCC as a co-diagnosis (2.6%), suggesting that clinicians may be anchoring on the well-publicized concept of Merkel cell carcinoma as a small, pearly papule in real-world practice.

Abstract P203: Milademetan is a potent, murine double minute 2 (MDM2) inhibitor, highly active in TP53 wild-type (p53WT) Merkel cell carcinoma (MCC) cell lines

Abstract Background: MCC is a highly aggressive neuroendocrine carcinoma of the skin with a poor overall prognosis. Current treatment options include surgery and radiation therapy for local MCC tumor and checkpoint blockade therapy for advanced disease. However, primary and acquired resistance can reduce response to therapy. Around 80% of all MCCs have integrated copies of Merkel cell polyomavirus (MCV). Virus-Positive MCC (MCCP) tumors typically contain few somatic mutations and express wild type (WT) p53 (TP53). In contrast, Virus-Negative MCC (MCCN) tumors have a high mutational burden, with a predominantly UV mutational signature. MCCP express two viral proteins: MCV small T antigen (ST) and a truncated form of large T antigen (LT). The MCV ST recruits MYCL and EP400 to form the SLaP complex that specifically activates several genes contributing to oncogenesis. A direct target of the SLaP complex is MDM2, an E3 ligase for p53. In p53WT MCCP, SLaP-dependent activation of MDM2 inhibits the tumor suppressive functions of p53. Here, we analyzed the efficacy of milademetan (RAIN-32), a potent, selective, and orally available MDM2 inhibitor, in MCC. Experimental procedures: Established MCCP cell lines with WT (MKL-1, WaGa, PeTa) or mutant p53 (MS-1), were treated with vehicle or several concentrations of milademetan or another MDM2 inhibitor AMG232 and cell viability was analyzed. Similar viability assays were also performed using MKL-1 p53 knockout (KO) cells and two newly established p53WT primary MCC cell lines. The p53 response in MCC cells treated with vehicle, milademetan or AMG232 was assessed by western blot (WB) analysis of p53 and its downstream effectors p21, PUMA and PARP-1. For in vivo testing, an initial tolerability study was conducted with once daily administration of milademetan by oral gavage in NSG mice. Milademetan activity was evaluated in MKL-1 xenograft and patient-derived xenograft (PDX) models in NSG mice. Pharmacodynamic markers of response in tumor samples from mice treated with vehicle or milademetan is analyzed by q-PCR and WB analysis. Summary of Results: Nanomolar concentrations of milademetan reduced cell viability of p53WT but not p53mutantMCCP MCC cell lines. Milademetan treatment increased levels of p21, PUMA and cleaved PARP-1 in MCCP cell lines MKL-1 and WaGa. Using p53 KO MKL-1 cells, we show that the effect of milademetan on MCC cell viability is p53 dependent. In vitro data show that milademetan is more potent than AMG232 in the context of MCC. Tolerability studies show that mice safely tolerate 100 mg/kg of milademetan. Milademetan treatment in the MKL-1 xenograft tumor model shows a dose-dependent response in tumor growth inhibition. In the DFMC-33043 PDX model, milademetan significantly inhibited tumor growth. Conclusion: Milademetan is a promising drug effective against p53WT MCC cell lines, xenograft, and PDX models. Ongoing in vivo testing of the anti-cancer cell activity of milademetan will provide evidence for clinical exploration of milademetan in MCC refractory to current therapies. Citation Format: Varsha Ananthapadmanabhan, Aine Knott, Kara M. Soroko, Prafulla C. Gokhale, Vijaya Tirunagaru, Robert Doebele, James A. DeCaprio. Milademetan is a potent, murine double minute 2 (MDM2) inhibitor, highly active in TP53 wild-type (p53WT) Merkel cell carcinoma (MCC) cell lines [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P203.

The texture of collagen in the microenvironments of Merkel cell carcinoma.

Solid tumors typically contain high levels of fibrillar collagen. The increased stromal collagen deposition usually promotes cancer progression since biochemical and biophysical cues from tumor-associated collagen fibers stimulate neoplastic cells. Few studies have investigated the relationship between Merkel cell carcinoma (MCC) and the extracellular matrix (ECM), but there are no works evaluating collagen.This is an observational, analytical, retrospective study including 11 patients with MCC. Primary tumor-stained sections were evaluated by second harmonic generation microscopy and texture analysis.Peritumoral texture features (area fraction, mean gray value, entropy, and contrast) showed much lower values than normal skin (P < .0001) revealing extensively altered structure of peritumoral collagen fibers. These differences were not significant between tumors with unfavorable and favorable known prognostic factors.Profound changes in collagen fibers present in the stroma accompanying primary MCC may contribute to the aggressive behavior of this tumor. Our results indicate that whatever MCC histological subtype, size or anatomical location, MCC promotes the same type of ECM for its development. As an outlook, therapies using ECM macromolecules or fibroblasts (the architects of ECM remodeling) as target could be useful in the treatment of MCC.