The extent of lymphadenectomy and overall survival depend on the timing of radiotherapy for rectal cancer.

Abstract

540 Background: Accurate staging and local disease control depend on the extent of lymphadenectomy (LAD) in rectal cancer. Previous studies suggest that lymph node (LN) number varies with neoadjuvant therapies. Our objectives were to measure the impact of timing of radiotherapy on extent of LAD and to determine the prognostic role of LN number in rectal cancer. Methods: Patients undergoing curative-intent surgery for rectal adenocarcinoma (1988-2006) in Los Angeles County were identified from the Cancer Surveillance Program. Patients were grouped according to radiotherapy timing (neoadjuvant, adjuvant, or none). To measure prognostic significance, an optimal cutoff was assessed for patients with N0 disease by dichotomizing LN numbers from 3-7. Results: Query of the registry identified 6,358 patients. Of these, 20% (n = 1,280), 25% (n = 1,573), and 55% (n = 3,545) received neoadjuvant, adjuvant, and no radiotherapy, respectively. There was no difference in LN number in patients with and without radiotherapy (7 vs. 8 LNs, p = NS). However, within the radiotherapy cohort, there was significantly lower LNs in the neoadjuvant group (5 vs. 9 LNs, respectively; p < 0.001). Survival differences favored the groups with higher LN number. The optimal LN cutoff with no survival difference was 7 in the adjuvant radiotherapy group; there was no optimal cutoff for neoadjuvant therapy patients. Conclusions: From our population-based cohort, we observed that patients receiving neoadjuvant radiotherapy had decreased LN retrieval and that LN number was non-prognostic. In contrast, the extent of LAD is a prognostic factor for overall survival in patients receiving adjuvant radiotherapy. [Table: see text] No significant financial relationships to disclose.