Lymph node retrieval after dissolution of surrounding adipose tissue for pathological examination of colorectal cancer.

Examination of >12 lymph nodes (LNs) is important for the diagnostic accuracy of nodal status following resection of colorectal cancer. In the present study, the efficacy of a fat dissolution technique for LN retrieval was evaluated using resected colon and rectum mesentery. First, the resected mesentery was searched for LNs by inspection and palpation immediately after surgery. Subsequently, fat dissolution liquid was applied to the remnant fat and the LN search was repeated. The primary endpoint was whether the second assessment would increase the number of evaluated LNs. Recruitment of 20 patients was planned. The study was conducted after institutional review board approval and written informed consent was obtained. Among 20 participants, 1 patient was excluded because LN dissection was not performed. The median number of LNs identified at the first and second assessments was 13 and 6, respectively, producing a significant increase in total LNs evaluated (13 vs. 20, respectively; P<0.01; paired t-test). One positive node was identified among the additionally identified LNs (0.9%, 1/107). The second assessment increased the number of LNs assessed to >12 in 4 patients, and although staging was not changed, the treatment was potentially altered in 2 stage II patients. The maximum diameter of the additionally obtained LNs was significantly smaller compared with those from the first assessment (4 vs. 7.7 mm, respectively; P<0.01; Wilcoxon signed-rank test). After the fat dissolution technique, the tumor cells were satisfactorily stained by carcinoembryonic antigen and cytokeratin-20. In conclusion, applying fat dissolution liquid to the remnant adipose tissue of the mesentery of the colon and rectum identified additional LNs. This method should be considered when insufficient LNs are identified after conventional LN retrieval.