The quandary of N0 disease after neoadjuvant therapy for rectal cancer.

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Improved outcomes after curative resection for rectal cancer have been driven in part by total mesorectal excision (TME) and the introduction of neoadjuvant chemoradiation. An equally important consideration in optimizing prognosis is accurate pathological staging, which is highly dependent on accurate assessment of lymph node status after TME. The use of neoadjuvant treatment impacts lymph node harvests and affects pathologic staging. Based on the anatomy of tumor cell spread along lymphatic pathways, Halsted was the first to suggest that en-bloc excision would provide the best chance of local and distant cancer control (1). This provides the basis of TME technique, as sharp dissection along the mesorectal fascia yields the entire mesorectum, which is the lymph nodebearing mesentery of the rectum. Secondarily, it removes any small regional metastases. Removing lymph nodes with the surgical specimen removes cancer cells, but more importantly provides information about staging, prognosis, and guides treatment decisions. For example, the United States Surveillance, Epidemiology and End Results (SEER) cancer registry database shows that for each T stage, 5-year overall and disease-free survival decreases with increasing LN involvement. The presence of lymph node metastases determines the patients most likely to benefit from adjuvant therapy (2).