Risk factors for lymph node metastasis in p/ypT1-2 rectal cancer

Background: This study aimed to identify and compare risk factors for lymph node metastasis in rectal cancer patients with and without neoadjuvant chemoradiotherapy. Methods: We retrospectively analyzed 1354 patients who underwent curative surgery, categorized into a Non-CRT group (pT1–2, n = 921) and a CRT group (ypT1–2, n = 433). Results: Lymph node metastasis occurred in 20.4 % of Non-CRT and 17.6 % of CRT patients. Independent predictors were lymphatic invasion (p < 0.001), tumor budding (p < 0.001), and pT2 stage (p = 0.002) in Non-CRT, and lymphatic invasion (p = 0.001) and venous invasion (p < 0.001) in CRT. Venous invasion showed a markedly stronger association in the CRT group (OR 12.102). Lymph node metastasis rates increased up to 64.3 % and 87.5 % with all risk factors, respectively. Conclusion: Risk factors for lymph node metastasis differed by CRT status, with venous invasion emerging as the key determinant in the CRT group.