Impact of the viability assessment of lateral lymph node metastasis in rectal cancer after neoadjuvant chemoradiotherapy.

Purpose: Preoperative chemoradiotherapy (CRT) followed by total mesorectal excision (TME) without lateral lymph node (LLN) dissection is widely performed for lower advanced rectal cancer. However, it is unclear whether residual cancer cells in the LLNs undergo apoptosis, disappear, or regrow if unresected.

Methods: Overall, 293 consecutive patients with T3/4 rectal cancer who underwent CRT followed by radical surgery between September 2003 and December 2018 were retrospectively reviewed. We assessed apoptosis of the residual primary tumor, mesorectum lymph nodes (MLN), and LLN using M30 cytoDEATH immunostaining and evaluated the degree of apoptosis. The difference in the prognosis of the lateral lymph node metastasis positive (LLNM +) and lateral lymph node metastasis negative (LLNM-) groups was assessed.

Results: There were 31 patients (10.6%) who were diagnosed with a complete response by hematoxylin and eosin (HE) staining. The residual cancer cells showed complete apoptosis in the primary lesion in 28 patients, in the metastatic MLN in only two patients, and in the metastatic LLN in one patient. The LLNM + group had a significantly poorer distant recurrence, recurrence-free survival, and overall survival than the LLNM- group.

Conclusion: The majority of the residual cancer tissue in LNs observed by HE staining was found to be non-apoptotic. If LLN metastasis is suspected on pretreatment imaging, performing LLN dissection together with TME should be considered.