OBJECTIVETo investigate the lymph nodes distribution and metastatic pattern of the ultra-low rectal cancer after neoadjuvant therapy.

METHODSA total of 21 rectal cancer gross specimen after neoadjuvant therapy and 23 rectal cancer gross specimen without neoadjuvant therapy were investigated by whole mount section and tissue microarray techniques with CK20. All the patients were treated by abdominoperineal resection.

RESULTSThere were 138 lymph nodes retrieved from the mesorectum in the neoadjuvant group including 39 metastatic lymph nodes and 12 micro-metastatic lymph nodes. Among these nodes, there were 7 rectal cancer cases with lymph nodes and 2 cases with micro-metastatic lymph nodes, and 6 cases had pathological complete remission. There were 415 lymph nodes retrieved from the mesorectum in the group without neoadjuvant therapy including 169 metastatic lymph nodes and 59 micro-metastatic lymph nodes. Among these nodes, there were 12 rectal cancer cases with lymph nodes and 4 cases with micro-metastatic lymph nodes. The proportions of metastatic lymph nodes in outer zone between the two groups were 21.5% and 29.0%, and those in pre-zone were 17.6% and 17.2% respectively. The ratio of metastatic lymph nodes in ischiorectal fossa between the two groups were 25.0% vs. 22.2% respectively. The rate of metastatic or micro-metastatic lymph nodes cases between the two groups were 4.8% vs. 13.0% respectively.

CONCLUSIONSThe lymph nodes distribution and metastatic pattern of the ultra-low rectal cancer are affected by neoadjuvant therapy. The proportions of the anal sphincter invasion and metastatic or micro-metastatic lymph nodes in ischiorectal fossa are lower after neoadjuvant therapy. Abdominoperineal resection as the standard treatment of the ultra-low rectal cancer after neoadjuvant therapy should be re-evaluated.