Radiotherapy for patients with resected tumor deposit-positive colorectal cancer: A surveillance, epidemiology, and end results-based population study

Context.-According to the American Joint Committee on Cancer's Cancer Staging Manual, 7th edition, TNM classification, tumor deposit (TD)-positive colorectal cancers (CRCs) are classified as N1c. The effects of radiotherapy and the effects of the updated American Joint Committee on Cancer 7th edition TNM N1c classification for patients with TD-positive CRC are unclear. Objective.-To investigate outcomes of radiotherapy in patients with resected TD-positive CRC. Design.-Resected TD-positive CRCs diagnosed from 2010 to 2014 were identified in the Surveillance, Epidemiology, and End Results 18 database. Factors associated with overall survival (OS) and cancer-specific survival (CSS) were investigated using Kaplan-Meier and Cox proportional hazards models. Results.-We included 2712 qualified CRC patients, who either underwent adjuvant radiotherapy (n=187; 6.9%) or received no radiotherapy (n = 2525; 93.1%). Univariate Cox proportional models showed improved CSS among all CRC patients who underwent adjuvant radiotherapy (CSS hazard ratio, 0.73; 95% CI, 0.57-0.95) and among rectal cancer patients when separated by location (hazard ratio, 0.57; 95% CI, 0.40-0.83), although these associations were attenuated in multivariable-adjusted models. There was improved OS among rectal cancer patients (hazard ratio, 0.77; 95% CI, 0.59-0.99). In subgroup analyses, radiotherapy was not associated with OS or CSS in either metastatic or nonmetastatic CRC patients. Instead, N1c category (versus N0) was associated with a worse OS (hazard ratio, 1.43; 95% CI, 1.31-1.57) but was not associated with CSS. Conclusions.-Radiotherapy did not independently improve OS among TD-positive CRC patients. In this study, classifying TD positivity as N1c was associated with worse OS than classifying TD positivity as N0. The findings seem to challenge the benefits of radiotherapy and the new N1c classification of TD for TD-positive CRC patients.