Predictors of Lymph Node Involvement in Rectal Cancer Patients Treated with Neoadjuvant Chemoradiotherapy

Abstract

Listen

Translate article

<h3>Purpose/Objective(s)</h3> Following neoadjuvant chemoradiotherapy (NART), some rectal cancer patients may have pathologic lymph node involvement (ypN+) despite complete response in the primary tumor, and should not be candidates for non-operative management. The aim of this study was to determine risk factors for ypN+ in rectal cancer patients treated with NART. <h3>Materials/Methods</h3> Data of rectal cancer patients treated with NART followed by surgery were evaluated. Patients with synchronous colon cancer, radiotherapy to surgery interval longer than 13 weeks, and those without lymph node (LN) dissection were excluded from the analysis. 92 patients were included. Median age was 59 (30-83). Female/male ratio was 35/57. Tumor location was proximal, mid- and distal rectum in 3, 45 and 44 patients, respectively. Tumor histology was adenocarcinoma in 79 patients, signet ring cell in 6 and mucinous carcinoma in 7. Clinical T stage was T2, T3 and T4 in 3, 81 and 8 patients, respectively. 90 patients had clinical LNs larger than 4 mm (10-34 mm: n=46). Median tumor and LNs SUV_max were 15 (3.9-46) and 2 (0.5-17.6), respectively. Median tumor GTV was 73 (28.9-370) ml. Median tumor length and thickness were 6 (3-14) cm and 16.5 (7-30) mm, respectively. All patients received 56 Gy to the primary tumor and 50.4 Gy to the lymph node regions, simultaneously in 28 fractions, and concurrent capecitabine. 27 patients had ypN+. Clinical and radiological features at initial presentation were analyzed to predict ypN+ using Chi-square or Mann-Whitney U tests. Logistic regression analysis was performed to determine the factors affecting ypN+. ROC analysis was performed to determine the cutoff values. <h3>Results</h3> Age (p=0.027), tumor SUV_max (p=0.001), largest clinical LN size (p=0.007) and number of LNs ≥10 mm in diameter (p=0.033) were significantly different between ypN0 and ypN+ patients in univariate analysis (Table). Only tumor SUV_max (HR (%95 CI): 0.828 (0.731-0.937), p=0.003) and largest clinical LN size (HR (%95 CI): 1.338 (1.023-1.750), p=0.033) were significant in multivariate analysis. Area under the ROC analysis curve (AUC) to determine ypN+ was 68.8% for LN size and 79.3% for tumor SUV_max. Cutoff values of LN size and tumor SUV_max for ypN+ were 10.5 mm (p=0.005) and 12.57 (p<0.001), respectively. Although ypN+ rates were higher in patients with signet ring cell (83%) and mucinous (43%) histology compared to adeno carcinoma (24%), it was not statistically significant. <h3>Conclusion</h3> Rectal cancer patients with lower tumor SUV_max and larger clinical lymph nodes at initial presentation are more likely to have pathologic lymph node involvement following neoadjuvant chemoradiotherapy.