Diagnosing occult tumour cells and their predictive value in sentinel nodes of histologically negative patients with colorectal cancer.

PURPOSE: Most studies on the sentinel node (SN) procedure in patients with colorectal cancer include immunohistochemical analysis of the SN only. To evaluate the real diagnostic accuracy of the SN procedure with immunohistochemical analysis, the presence of occult tumour cells in all histologically negative lymph nodes was compared to the presence of these cells in SNs. Also the reproducibility of diagnosing occult tumour cells (OTC) and the sensitivity of three different antibodies was assessed. METHODS: Between November 2006 en July 2007, an ex vivo SN procedure was performed in 58 histologically N0 patients with colorectal cancer. All lymph nodes (n = 908, mean 15.7) were step-sectioned and immunohistochemistry was performed using two antibodies against cytokeratins (Cam5.2, and CK 20) and one antibody against BerEp-4. RESULTS: OTC were identified in 19 of 58 patients, with micrometastases (0.2-2 mm) in 7 and isolated tumour cells (ITC)(<0.2 mm) in 12 patients. The overall agreement in diagnosing OTC between two independent pathologists was 86%. An SN was identified in 53 of 58 patients. All micrometastases were found in SNs. In two patients with negative SNs, ITC's were demonstrated in non-SNs (sensitivity 88%, and overall accuracy 96%). CONCLUSION: Additional immunohistochemical analysis of histologically negative lymph nodes demonstrates occult tumour cells in 33% of the patients resulting in an upstaging rate of 12%. Occult tumour cells are predominantly found in the SN, therefore SN mapping has the potential to refine the staging system for patients with colorectal cancer.

Improving staging accuracy in colon and rectal cancer by sentinel lymph node mapping: a comparative study.

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.