Designing a practice-changing trial for a rare cancer population: The Rational MCC trial of first definitive treatment for Merkel cell carcinoma

Background: People with rare cancers need evidence-based treatment. Trials require large samples to disprove no difference in treatment effect. Rare cancers, like commoner malignancies, can be diverse affecting population selection and stratification in trial design and applicability of results. The aggressive skin cancer, Merkel cell carcinoma (MCC) affects <300, predominantly elderly, UK patients annually. Standard management with surgery and/or radiotherapy for loco-regional MCC is based on retrospective data.