Objective: To investigate the occult lymph node metastasis in the middle and lower third rectal cancer after neoadjuvant radiotherapy.
Methods: From June 2003 to December 2006, 74 rectal cancer patients received neoadjuvant radiotherapy (30 Gy/10 f/2 w, CACA-CRC-001) and underwent total mesorectal excision (TME) two weeks later. Fat clearance technique was used in all the samples. Occult lymph node metastasis was detected in the mesorectum using the anti-CK antibody.
Results: In total 1883 retrieved lymph nodes, 172 metastasis lymph nodes were harvested by HE examination with the mean diameter [(4.9+/-2.6) mm] being larger than that (2.7+/-1.4) mm of the 1711 negative nodes (P<0.01). In HE negative nodes, occult metastasis was found in 40 lymph nodes (2.33%) from 24 patients. Most of these nodes were less than 5 mm (90.0%) with a mean diameter of (3.2+/-1.2)mm, smaller than those of HE-positive metastasis nodes (P<0.01). Occult metastasis was found in 23.1% (9/39) of HE-negative patients. Occult metastasis incidence was higher in patients with HE-positive nodes (42.8%,P<0.01). No correlation of lymph node occult metastasis with tumor differentiation, age, or surgical procedures was found. There was no significant difference in recurrence-free survival between ypN(0) patients with and without occult metastasis (P=0.157).
Conclusion: It is not necessary to include occult lymph node metastasis in the TNM staging in patients with ypN(0) rectal cancer.