Aim: To compare the predictive value of sentinel lymph node (SN) mapping between patients with colon and rectal cancer.
Patients and methods: An ex vivo SN procedure was performed in 100 patients with colon and 32 patients with rectal cancer. If the sentinel node was negative, immunohistochemical analyses using two different antibodies against cytokeratins (Cam5.2 and CK 20) and one antibody against BerEp-4 were performed to detect occult tumour cells. Isolated tumour cells (<0.2mm) were discriminated from micrometastases (0.2-2mm).
Results: An SN was identified in 117 patients (89%), and accurately predicted nodal status in 106 patients (accuracy 91%). Both sensitivity and negative predictive value were higher in colon carcinomas than in rectal carcinomas (83% versus 57%, p=0.06 and 93% versus 65%, p=0.002 respectively). In patients with extensive lymph node metastases the SN procedures were less successful. Eleven of the 13 unsuccessful SN procedures were performed in patients with rectal cancer who had pre-operative radiotherapy. After immunohistochemical analysis 21 of the 73 N0 patients had occult tumour cells in their SN; eight patients had micrometastases and 13 patients had isolated tumour cells.
Conclusion: SN mapping accurately predicts nodal status in patients with colonic cancer. Immunohistochemical analysis demonstrates micrometastatic disease in eight out of 73 N0 patients, with a true upstaging rate of 11%. SN mapping is less reliable in patients with rectal cancer after pre-operative radiotherapy.