Occult tumor metastasis and the prognostic value of sentinel lymph nodes in rectal cancer.

The aim of the present study to evaluate the application of sentinel lymph node (SLN) pathology in rectal cancer using ex vivo mapping and to investigate the incidence and prognostic value of occult SLN metastasis in routine node-negative specimens. Specimens (n=117) of rectal cancer were examined using a combination of routine pathology and ex vivo SLN mapping. The inspected SLNs were further treated with immunohistochemical staining for occult cancer foci. The log-rank test was used to assess survival. SLNs were examined in 112 of the included specimens with a total number of 212, resulting in an identification rate of 95.7% (112/117). The status of SLNs accurately reflected N stage in 93.8% (105/112) of cases and the sensitivity was 75.6% (31/41) in detecting nodal metastasis. The accuracy of SLN pathology decreased in cancers of more advanced TNM stages (P=0.001). In 74 cases with routine node-negative (N0) disease, SLN micrometastasis (MIC) and isolated tumor cells (ITC) were examined in 9 and 4 cases, while the remaining 61 were regarded as negative (NEG). The log-rank test revealed poorer disease-free and overall survival of the MIC group compared with the NEG group. However, the findings from the ITC group were not significant compared with those from the MIC and NEG groups. In conclusion, ex vivo SLN pathology is practical and accurate in rectal cancer; however, its utility is limited in cases of advanced disease. Immunohistochemically detected SLN micrometastasis in node-negative cases is therefore a predictor of poorer outcome, and may therefore be listed as a marker for adjuvant therapy.