Evaluation of lymphadenectomy in patients receiving neoadjuvant radiotherapy for rectal adenocarcinoma

Background. Accurate pathologic staging has been shown to correlate with outcome in rectal cancer. Because the exact number of examined lymph nodes (LNs) may vary with preoperative therapies, our objective was to measure the impact of neoadjuvant radiation on LN number for rectal adenocarcinoma. Methods. Patients who underwent curative-intent radical surgery for rectal adenocarcinoma in Los Angeles County (LAC) were identified from the Cancer Surveillance Program (CSP) of California (1988 - 2006). Patients were grouped according to receipt of radiotherapy (neoadjuvant or none), and the number of examined LNs was assessed. Results. Query of CSP identified 2,727 patients meeting eligibility criteria; 70 and 30 % of patients received no radiotherapy or neoadjuvant radiotherapy (NRT), respectively. When comparing LNs, a lower mean number was observed in the neoadjuvant group than the no-radiation group (7 vs. 8.9 LNs, respectively; p<0.001). When matching the cohorts for age and sex, the neoadjuvant group still had fewer examined LNs (7.1 vs. 9.8, respectively, p<0.001). In patients who received NRT, no optimal LN number was associated with improved survival. However, on subset analysis of patients with N0 disease, a LN number of C8 was associated with best rates of 5 year and overall survival. Conclusions. Within the LAC population, we observed a lower number of LNs retrieved in patients receiving radical surgery for rectal cancer than guideline recommendation. This number is reduced further in those who received NRT independent of age and sex. Our results highlight the limitations in adhering to minimum LN requirements for rectal cancer when NRT is provided.