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.
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