Effects of neoadjuvant chemotherapy plus chemoradiotherapy on lymph nodes in rectal adenocarcinoma

The pathological nodal stage, determination of which requires examination of ≥ 12 lymph nodes, is one of the main prognostic factors in rectal cancer. Neoadjuvant chemoradiotherapy (CRT) may reduce the number of both lymph nodes retrieved and positive lymph nodes. Induction chemotherapy before CRT aimed at reducing the rate of distant metastases. However, the impact of this new treatment on number of lymph nodes retrieved and positive lymph nodes is unknown. This study was performed to evaluate the effects of neoadjuvant chemotherapy on lymph nodes in locally advanced rectal cancer treated by CRT. We retrospectively included patients with T2 - 4 Nx M0 rectal cancer and compared those receiving neoadjuvant chemotherapy plus CRT with those receiving CRT alone. From 2012 to 2019, 85 patients were treated with neoadjuvant chemotherapy + CRT and 189 with CRT alone. The number of lymph nodes retrieved (19 vs. 17, respectively, P = 0.434), the rate of specimens with ≥ 12 lymph nodes (92% vs. 88%, respectively, P = 0.397), and the median number of positive lymph nodes (1 vs. 2, respectively, P = 0.878) were similar between the two groups. However, the rate of pN0 was higher after neoadjuvant chemotherapy + CRT compared to CRT (75% vs. 62%, respectively, P = 0.030). Neoadjuvant chemotherapy before CRT for locally advanced rectal cancer did not modify the number of lymph nodes retrieved or the number of positive lymph nodes compared to CRT alone. However, it significantly increased the rate of tumors without any positive lymph nodes (ypN0).