Optimizing radiation therapy for merkel cell carcinoma: evaluating prognostic factors and treatment outcomes

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine skin cancer. Surgery and radiation therapy (RT) are common treatment options; however, an optimal RT strategy has yet to be established. Therefore, the present study examined the outcomes of MCC patients treated with RT, with the aim of elucidating current RT practices and identifying prognostic factors for RT optimization.

This was a retrospective analysis of 32 non-metastatic MCC patients treated with RT. Local control (LC), progression-free survival (PFS), and overall survival (OS) rates were calculated using the Kaplan-Meier method. The Log-rank test was used to examine the effect of each factor on outcomes.

Median age was 80 years, with a median follow-up period of 26 months. The median dose was 52 Gy in 26 fractions and combined with surgery in 23 patients. Two-year LC, PFS, and OS rates were 94, 61, and 74%, respectively. The Log-rank test showed that tumor size ≥ 5 cm was associated with worse LC (p = 0.03). Male sex and the absence of surgery correlated with worse PFS (p = 0.047 and 0.023, respectively). Performance status ≥ 2, the absence of surgery, and RT margin < 3 cm correlated with worse OS (p = 0.006, 0.02, and 0.02, respectively). RT dose, intensity-modulated RT, and elective nodal irradiation were not associated with any outcomes in this population.

RT achieved high local control; however, the metastasis rates were high. A wide RT margin and the combination of RT with surgery may improve the outcomes of MCC patients.