Aim:

Merkel cell carcinoma (MCC) is a highly aggressive and radiosensitive neuroendocrine tumour. Radiotherapy (RT) has multiple roles in the treatment of MCC, from definitive management to palliation; when used alone, or combined with chemotherapy (chemo-RT). We aim to determine the in-field control rates achieved with Radiotherapy (RT) or chemotherapy-radiotherapy (chemo-RT) and the patterns of relapse following such treatment.

Methods and Materials:

Patients treated with RT or chemo-RT for biopsy confirmed MCC were retrospectively evaluated. Definitive treatment was defined as treatment for macroscopic or residual microscopic (positive margins following surgery).Adjuvant treatment was defined as following microscopically clear excision or close margins.
Patients’ medical records (electronic and paper) were reviewed to collect data on diagnosis, staging, treatment details (including intent) and outcome (dates of death or date and status at last consultation). Patients with metastatic disease were excluded.

Results:

Of the 55 patients treated with RT alone (n=39) or chemo-RT (n=16), 32 (59%) were disease free with a median follow up time of 25 months (2-165 months). 3 year LRFS, DMFS and OS were 85%, 64% and 70%. Chemotherapy use was not significantly correlated with disease control or survival. Of 23 relapses, 19 were distant. Four of 19 experienced in-field or in-transit failure(with distant failure simultaneously). Four patients experienced “out of field” loco-regional recurrence. Of the in-field recurrences (n=4), 3 occurred in patients with macroscopic nodal metastases at presentation. Two of whom were treated with definitive RT (both received 54Gy), whilst 1 patient had chemo-RT (56Gy) to their nodal disease.

Conclusion:

RT with or without chemotherapy provides excellent in–field disease control in the treatment of primary and regionally metastatic MCC. As the risk of disease recurrence in patients with MCC is largely systemic, RT achieves loco-regional disease control.