Risk factors and therapeutic significance for inguinal lymph node metastasis in advanced lower rectal cancer.

120 Background: Which patients with lower rectal cancer are at risk of inguinal lymph node metastasis (ILNM) and how to treat ILNM remain unclear. This study aimed to clarify the predictors of ILNM and clinical significance of treatment for ILNM. Methods: Consecutive patients with rectal adenocarcinoma invading the anal canal who underwent curative surgery between 2003 and 2019 at a single institution were retrospectively reviewed. The pathological nodal involvement in mesorectal, lateral pelvic or inguinal lymph nodes (ILN) at the time of rectal surgery and of later onset were collectively defined as final nodal metastasis (f-LNM) in this study. Factors associated with f-LNM were analyzed. Moreover, the ‘modified therapeutic value index’ defined by the 5-year overall survival rate of patients treated against f-LNM multiplied by their frequency was calculated for each lymph node area. Results: A total of 145 patients were enrolled, among whom16 patients developed ILNM. For predicting f-ILNM, the cutoff 8.5 mm of ILN diameter gave area under the curve of 0.889. Dentate line involvement and ILN larger than a simplified cutoff of 8 mm were independently associated with the development of ILNM (odds ratio: 33.4 and 11.9, respectively). The modified therapeutic value indice of inguinal, lateral pelvic and mesorectal LNs in the entire population were 6.1, 8.2 and 20.3 points, respectively. In patients with dentate line invaded by cancer, they were 11.7, 5.8 and 16.2 points, respectively. Moreover, the index of ILN was 21.1 points when confined to patients with ILN larger than 8 mm. Conclusions: Dentate line involvement and ILN larger than 8 mm were predictive of developing ILNM in patients with rectal cancer invading the anal canal. Treatment of ILNM may be recommended for patients manifesting the above predictors, given the significant therapeutic outcomes.