Survival Impact of Time to Initiation of Adjuvant Radiation for Merkel Cell Carcinoma: An Analysis of the National Cancer Database.

PURPOSE: This study aimed to determine the impact of time to initiation (TTI) of adjuvant radiation therapy (RT) on overall survival (OS) for patients with stage I or II Merkel cell carcinoma (MCC).

METHODS AND MATERIALS: The National Cancer Database was queried for patients with MCC of the head and neck, trunk, or extremities diagnosed between 2006 and 2014. Patients who did not undergo resection or receive adjuvant RT within 180 days of surgery were excluded. TTI was defined as the time from resection to first RT fraction. Linear regression was used to define factors associated with TTI. Recursive partitioning analysis modeling was performed to determine an optimal threshold for TTI. Cox proportional hazards modeling was performed to define covariates associated with OS.

RESULTS: A total of 2293 patients were included in this study. The median TTI for the cohort was 62 days (interquartile range, 43-86 days). TTI was not associated with OS for the overall cohort by multivariable Cox modeling (P = .19). Age, treatment facility type, lymph node examination, anatomic subsite, and surgical margin were associated with TTI (P < .05). Age, sex, insurance status, Charlson-Deyo comorbidity score, lymph node examination status, tumor size, and surgical margin were associated with OS (all P < .05).

CONCLUSIONS: Increased TTI of adjuvant RT was not associated with OS for patients with early stage MCC in this analysis of the National Cancer Database. The median TTI of 62 days from resection to adjuvant RT initiation for our study cohort contextualizes TTI on a national level and may offer reassurance for patients with prolonged postoperative wound healing or intercurrent illness delaying immediate RT initiation. Despite the lack of a clear detriment to survival with increased TTI up to 180 days from surgery, unnecessary delays in initiating adjuvant therapy should continue to be minimized while ensuring optimal recovery from resection.