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Carcinoma, Merkel Cell

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Merkel Cell Carcinoma

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Pembrolizumab

Antineoplastic Agents, Immunological

Immune Checkpoint Inhibitors

Patients receive pembrolizumab IV over 30 minutes on day 1. Treatment repeats every 21 days for up to 17 cycles in the absence of disease progression or unacceptable toxicity. Patients may also undergo standard of care radiation therapy within 14 days of day 1, cycle 1. Patients undergo PET-CT, CT, or MRI throughout the trial. Patients may also undergo blood sample collection as clinically indicated at the discretion of the treating investigator.

Patients receive standard of care observation every 3 months for 1 year, and then every 6 months for 5 years. Patients may also undergo standard of care radiation therapy within 14 days of day 1, cycle 1. Patients undergo PET-CT, CT, or MRI throughout the trial. Patients may also undergo blood sample collection as clinically indicated at the discretion of the treating investigator.

Best Practice

Biospecimen Collection

Computed Tomography

Magnetic Resonance Imaging

Positron Emission Tomography

Radiation Therapy

Janice Mehnert

This phase III trial studies how well pembrolizumab works compared to standard of care observation in treating patients with stage I-III Merkel cell cancer that has been completely removed by surgery (resected). Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread.

PRIMARY OBJECTIVE:

I. To compare recurrence free survival (RFS) and overall survival (OS) as co-primary endpoints across the two arms.

SECONDARY OBJECTIVES:

I. To evaluate adverse events. II. To evaluate distant metastasis free survival (DMFS). III. To evaluate the impact of radiation on clinical outcomes (OS, RFS, DMFS).

OUTLINE: Patients are randomized to 1 of 2 arms.

ARM A: Patients receive pembrolizumab intravenously (IV) over 30 minutes on day 1 of each cycle. Treatment repeats every 21 days for up to 17 cycles in the absence of disease progression or unacceptable toxicity. Patients may also undergo standard of care radiation therapy within 14 days of day 1, cycle 1. Patients undergo positron emission tomography (PET)-computed tomography (CT), CT, or magnetic resonance imaging (MRI) throughout the trial. Patients may also undergo blood sample collection as clinically indicated at the discretion of the treating investigator.

ARM B: Patients receive standard of care observation every 3 months for 1 year, and then every 6 months for 5 years. Patients may also undergo standard of care radiation therapy within 14 days of day 1, cycle 1. Patients undergo PET-CT, CT, or MRI throughout the trial. Patients may also undergo blood sample collection as clinically indicated at the discretion of the treating investigator.

After completion of study treatment, patients are followed up every 3-6 months for 5 years from the date of registration.

Testing Pembrolizumab Versus Observation in Patients With Merkel Cell Carcinoma After Surgery, STAMP Trial

STAMP: Surgically Treated Adjuvant Merkel Cell Carcinoma With Pembrolizumab, a Phase III Trial

An intention-to-treat (ITT) analysis using the stratified log-rank test will be performed to compare overall survival (OS) and RFS between the two arms.

An ITT analysis using the stratified log-rank test will be performed to compare OS and RFS between the two arms.

RFS in each arm will be evaluated by radiation treatment status (radiation versus \[vs.\] no radiation therapy). The analysis will be a planned post-hoc analysis with primary goal of examining whether use of post-operative radiation therapy is associated with RFS. Cox multivariate models for RFS will be developed to evaluate the impact of radiation therapy while adjusting for pembrolizumab treatment and clinical/ pathological factors. The treatment fields and dose data will also be included in the Cox model as covariates. Secondary analyses for radiation therapy (RT) will examine factors associated with use of post-operative RT. Multivariate logistic regression models (radiation therapy vs. no radiation therapy) will be developed to evaluate the associations with demographic, clinical/pathologic, and treatment-related factors and pembrolizumab treatment.

OS in each arm will be evaluated by radiation treatment status (radiation vs. no radiation therapy). The analysis will be a planned post-hoc analysis with primary goal of examining whether use of post-operative radiation therapy is associated with OS. Cox multivariate models for OS will be developed to evaluate the impact of radiation therapy while adjusting for pembrolizumab treatment and clinical/ pathological factors. The treatment fields and dose data will also be included in the Cox model as covariates. Secondary analyses for radiation therapy will examine factors associated with the the use of post-operative RT. Multivariate logistic regression models (radiation therapy vs. no radiation therapy) will be developed to evaluate the associations with demographic, clinical/pathologic, and treatment-related factors and pembrolizumab treatment.

DMFS will be evaluated by treatment arms. If there is no distant metastasis, cases will be censored at the time of last assessment.

Measured per Common Terminology Criteria for Adverse Events version 5.0. Adverse events from each arm will be summarized and compared using Fisher's exact test.

Spots Global Cancer Trial Database for pathologic stage i cutaneous merkel cell carcinoma ajcc v8