What is the incidence of metastatic lymph node involvement after significant pathologic response of primary tumor following neoadjuvant treatment for locally advanced rectal cancer?

BACKGROUND: In locally advanced rectal cancer (LARC) patients, major response to neoadjuvant radiotherapy (NR) has been associated with favorable long-term outcomes. Positive pathologic nodal status was recently proven to be associated with poor prognosis even after total regression of primary tumor (ypT0). The aim of this study was to evaluate the rate of lymph node (LN) involvement in patients with complete (ypT0) or major (TRG1: very few viable tumor cells) response.
METHODS: Included were patients with complete or major response after radiotherapy followed by surgery and histological examination of the whole specimen.
RESULTS: From 1996 to 2010, 245 patients with LARC were treated by NR. We collected clinical data for 53 patients (21.6 %) with ypT0 (n = 26, 49 %) or TRG1 (n = 27, 51 %) response. Sphincter-preserving surgery was performed in 40 patients (75 %). Overall, nine patients (16.9 %) presented LN involvement: 2 (7.7 %) in the ypT0 group and 7 (25.9 %) in the TRG1 group (NS). Patients with ypT3 tumors had significantly more invaded LN than patients with ypT1-T2 tumors (6 of 13 [46 %] vs 1 of 14 [7 %], p = .032). After median follow-up of 30 months (range, 1-160 months), 5-year disease-free and overall survivals were 88.2 and 89.0 %, respectively.
CONCLUSIONS: There was a clear cutoff between patients with ypT0-T2 (3 of 40, 7.5 %) and ypT3 (6 of 13, 46 %) concerning the incidence of metastatic LN in patients achieving pathologic complete or major response after NR. In patients with good clinical response, local full-thickness resection of the residual tumor could be a first step, followed by standard rectal resection in cases of ypT3.