Long-term outcomes after surgical dissection of inguinal lymph node metastasis from rectal or anal canal adenocarcinoma

BACKGROUND: The 8th edition of the tumor-node-metastasis (TNM) classification classifies inguinal lymph nodes as regional lymph nodes for anal canal carcinoma but non-regional lymph nodes for rectal carcinoma. This difference might reflect the different prognosis of inguinal lymph node metastasis from anal canal carcinoma and rectal carcinoma. However, long-term outcomes of inguinal lymph node metastasis from rectal or anal canal adenocarcinoma are unclear, which we aimed to investigate in this study. METHODS: The study population included 31 consecutive patients with rectal or anal canal adenocarcinoma who underwent inguinal lymph node dissection with curative intent at the National Cancer Center Hospital from 1986 to 2017. Long-term outcomes were assessed and clinicopathologic variables analyzed for prognostic significance. RESULTS: Of the 31 patients, 12 patients had rectal adenocarcinoma and 19 patients had anal canal adenocarcinoma. Synchronous metastasis were observed in 14 patients and metachronous metastasis in 17 patients. After dissection of inguinal lymph node metastasis with curative intent, the 5-year overall survival rate was 55.2%, with 12 patients surviving for more than 5 years. Median survival time was 66.6 months. Multivariate analyses revealed that location of primary tumor (rectum versus anal canal) was not a prognostic factor, whereas lateral lymph node metastasis and histological findings were independent prognostic factors. CONCLUSION: Given the good prognosis, inguinal lymph node metastasis in patients with rectal or anal canal adenocarcinoma appears to be regional rather than distant. If R0 resection can be achieved, inguinal lymph node dissection may be indicated for these patients.