Acetone clearance of mesocolic or mesorectal fat increases lymph node yield and may improve detection of high-risk Stage II colorectal cancer patients

Aim Lymph node (LN) status is key to determining the need for adjuvant therapy in colorectal cancer (CRC) and for disease which has progressed to Stage II (T3-T4, N0, M0). A yield of fewer than 12 LNs is considered a risk factor similar to high-grade histology and vascular, lymphatic and perineural invasion. The aim of this retrospective study was to investigate the effect of acetone fat clearance of the mesocolon or mesorectum on LN yield and the identification of patients with high-risk Stage II CRC. Method Results After conventional LN retrieval, fatty tissue derived from the mesocolon or mesorectum of 80 CRC specimens was incubated in acetone for 24 h. A second dissection was then performed by a trained technician. The total number of LNs as well as tumour involvement (LNpositive and LNnegative) were assessed at each stage. In addition, LN morphology was assessed and clinicopathological data were extracted from existing pathology reports. Eighty CRC specimens were available for study. 1548 (94%) LN were negative and 96 (6%) were positive. The median (range) LN yield per specimen was 12 (3-41) LN increasing to 18 (4-48) LN after fat clearance (P <0.001). After fat clearance, 534 additional LNs were identified in 75 (94%) of the specimens, and all but 10 were negative. The pN stage did not change in six patients who were found to be LN positive after fat clearance. However, the number of high-risk Stage II CRC patients decreased from 11 to 7. Although important for these patients, this downstaging did not reach statistical significance (P = 0.125). Conclusion Acetone clearance of mesocolic or mesorectal fat increases median LN yield and may in a larger study decrease the number of patients classified as having high-risk Stage II CRC.