Sentinel node in skin melanoma: Application of immunohistochemistry into micrometastases detection.

B27

Introduction: The sentinel node biopsy has become a standard method of evaluation of the degree of progression in skin melanoma. Histopathological evaluation plays a key role in this process. One of the methods which increases the sensitivity of detecting micrometastases in sentinel nodes is the immunohistochemical examination of specimens. It enables identification of the patients in whom micrometastases were not detected in a standard H+E examination. The aim of work: The influence of the immunohistochemical examination of the sentinel node on the evaluation of the degree of progression of skin melanoma. Material and methods: The specimens of sentinel nodes taken from 110 patients treated in the 1^st Department of Surgical Oncology, Wielkopolska Oncological Centre in 2004/05 were subjected to evaluation. Skin melanoma was diagnosed in the patients, but in the H+E examination no metastases were found. According to Breslow classification 30 patients had lesions of ≤1 mm, 36 patients - between 1.01 and 2mm, 26 patients - between 2.01 and 4mm and 18 patients - of > 4mm. If the sentinel node have contained metastases detected in either a pathological or immunohistochemical examination, the patient would be subjected to lymphadenectomy. Sections were made of all sentinel node specimens, which were then subjected to an immunohistochemical examination with the application of the En Vision/HRP complex. Monoclonal antibodies anti HMB45 and anti MelanA and a polyclonal antibody anti S-100 were applied to detect melanoma cells. Findings: In the group of 110 patients with the negative result of the H+E examination in 11 patients (10%) positive results of the immunohistochemical examinations were found. However, in this group 1 patient had a negative result of the S-100 and HMB-45 stains with a positive MelanA stain and 1 patient had a negative MelanA stain with positive S-100 and HMB45 results. Additionally in the analysed group in 6 (5.5%) patients naevi cells were found. In the immunohistochemical examination they showed HMB45 expression and no S-100 nor MelanA expression. Conclusions: The application of the immunohistochemical examination enabled identification of metastases to the sentinel node in 10% of the patients with the negative result of the H+E examination. We think that the simultaneous application of three markers (S-100, HMB45 and MelanA) makes it possible to avoid false negative results.