Abstract. 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.
IntroductionSurgery remains the first choice of treatment for patients with rectal cancer and prognosis mainly depends on the stage of disease at the time of surgery (1). At present, the most valuable staging and prognostic indicator is lymph node status, i.e., whether the lymph nodes are involved in cancer or not (2,3). Therefore, it is widely accepted that examination of a sufficient number of lymph nodes is essential for accurate staging, thus aiding prescription for adjuvant therapy (4,5).However, examination of the sentinel lymph node (SLN), defined as the node with the highest incidence of metastasis, was reported as being capable of reducing the pathological workload while maintaining diagnostic accuracy. If the results of SLN examination in breast cancer and melanoma could be duplicated in rectal cancer the effort and cost of harvesting an adequate number of nodes would no longer be necessary (6,7). The present study therefore aimed to evaluate the application of SLN pathology in rectal cancer by mapping with patent blue V dye.In addition, recurrence has been observed in those patients presenting with primarily node-negative disease, indicating that routine pathological examination may fail to detect certain occult tumor metastases (8,9). Identification of these foci may aid the subdivision of node-negative patients for subsequent treatment to prevent relapse (10). Moreover, although the SLN of colo...