Timeliness of post-operative radiation therapy may affect Merkel cell carcinoma recurrence

Key takeaways:

• Five-year locoregional recurrence increased when time to initiate post-operative radiation therapy went beyond 8 weeks (28%).
• Locoregional recurrence usually occurred beyond the radiation field.

Delaying post-operative radiation therapy for the treatment of Merkel cell carcinoma beyond 8 weeks significantly increased patients’ risk for locoregional recurrence, according to a study.

“Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine skin cancer with an incidence of approximately 3,000 cases a year in the United States, and is rapidly increasing,” Nora A. Alexander, BS, of the department of medicine in the division of dermatology at University of Washington, and colleagues wrote.

MCC is often treated with surgery and post-operative radiation therapy (PORT); however, researchers have not yet evaluated if there is an optimal time interval between surgery and the initiation of PORT.

In this retrospective study, the authors utilized competing risk regression to evaluate the associations between the time PORT was initiated and the locoregional recurrence of stage 1 or 2 MCC. The competing risks included metastasis and death.

Results showed that the median time to initiate PORT was 41 days (range, 8 to 125 days) and a median follow-up of 55 months.

Of the 124 patients, 17 experienced locoregional recurrence of which 14 arose outside the radiation field, defined as taking place within or beyond the 50% prescription isodose line.

The risk for locoregional recurrence at 5 years was higher for patients whose time to initiate PORT was greater than 8 weeks compared with initiation at 8 weeks or less (28% vs. 9.2%; P = .006).

For every week that PORT was delayed, the risk for locoregional recurrence increased by 20% (P = .002).

The cumulative incidence of MCC-specific death was also associated with the increase of time to initiate PORT with a hazard ratio of 1.14 per 1-week increase (P = .016).

“These data suggest PORT should be initiated as early as feasible, ideally within 8 weeks of definitive surgery,” the authors recommended.