The effect of neoadjuvant therapy on the size, number, and distribution of mesorectal lymph nodes

The current therapeutic approach to patients with locally advanced rectal cancer is neoadjuvant radiotherapy or chemoradiotherapy followed by total mesorectal excision. We aimed to investigate the number, size, and distribution of metastatic and nonmetastatic lymph nodes within the mesorectum; whether neoadjuvant therapy has any impact on the number and size of the lymph nodes; and the impact of metastatic lymph node localization on overall and disease-free survival. Specimens from 50 consecutive patients with stage II/III rectal cancer receiving either neoadjuvant radiotherapy or chemoradiotherapy were investigated. Lymph node dissection was carried out by careful visual inspection and palpation. The localization of the each lymph node within the mesorectum and the relation with the tumor site were noted. The size and the number of lymph nodes retrieved decreased significantly with neoadjuvant therapy. Majority of the metastatic and nonmetastatic lymph nodes were located at or proximally to the tumor level and posterior side of the mesorectum. No relation was observed between the overall and disease-free survival, and the localization of the metastatic lymph nodes. Presence of lymph node metastases proximal to the tumor level has no impact on survival compared with the presence of lymph node metastasis only in the peritumoral region of the mesorectum. Although neoadjuvant therapy decreases the size and the number of lymph nodes, reaching an ideal number of lymph nodes for accurate staging is still possible with careful naked eye examination and dissection of perirectal fat. As the majority of metastatic and nonmetastatic lymph nodes are located in peritumoral and proximal compartment, and posterior side of the mesorectum, these regions should be the major interest of dissection.