Good and complete responding locally advanced rectal tumors after chemoradiotherapy: where are the residual positive nodes located on restaging MRI?

Purpose: Aim of this study was to evaluate the distribution of persistent mesorectal lymph node metastases on restaging MRI in patients with a good or complete response of their primary tumor (ypT0-2) after CRT for locally advanced rectal cancer. Methods: Two hundred and twenty eight locally advanced rectal cancer patients underwent CRT, which resulted in a good response (downstaging to yT0-2) in 144 patients. Forty-nine patients were excluded (no surgery/insufficient follow-up or lacking lesion-by-lesion histology results). This resulted in a final study group of 95 yT0-2 patients. For the patients with a yN(+)-status, a detailed lesion-by-lesion comparison between restaging MRI and histology was performed to evaluate the characteristics and distribution of the individual N+-nodes. Results: 7/95 patients (7%) had a yT0-2N(+) status (11/880 (1%) N+ nodes): no N+ were found below the tumor level, 55% of the N+ nodes were located at the level of the tumor, and 45% proximal to the tumor (at a median distance of 1.4 cm above the tumor level). In axial plane, 82% of the nodes were located at the ipsilateral circumference of the tumor, at a median distance of 0.9 cm from the tumor/rectal wall. Conclusions: The incidence of persistent metastatic mesorectal nodes after CRT in patients with a good tumor response after CRT is very low. No N+ nodes are found below the tumor level. All N+ nodes are located at the level of or proximal to the primary tumor, of which the majority very close to the tumor/lumen.