Pathology of Sentinel Lymph Nodes for Merkel Cell Carcinoma

Background: In the present work, we evaluated the possibility of introducing ultrasonographic (US) examination in association to fine needle aspiration cytology (FNAC) before sentinel lymph node biopsy (SLNB) as a useful diagnostic tool in the pre-surgical management of patients with MCC and we also assessed the negative predictive value and false negative rate of combined cytological (US+FNAC) and histological (SLNB) procedure compared to the literature values obtained from different SLNB procedures. Design: US examination was performed in 53 patients with diagnosed MCC and in 11 patients it was followed by FNAC of US suspicious lymph node. Smears were examined by routine cytological staining. Cases of uncertain diagnosis were stained in immunocytochemistry with a combination of anti-cytokeratin antibodies (CK 20, CAM 5.2). Results: All FNAC were informative (10 LNs were positive for metastases, 1 was negative). Of all others 42 MCC cases, with nonsuspicious lymph nodes on US, in which no FNAC examination was performed, 6 carcinomas (14.3%) turned out to be lymph node positive on histological examination. One of the 11 (9.1%) negative cytological diagnoses was false negatives since lymph node metastasis of 5 mm of diameter was found by SLNB on histology. Based on these data, US+FNAC are endowed with high sensitivity and accuracy (both of 90.9%) and absolute specifi city (100%) and we suggest that US examination should be performed in all patients with MCC adding immunocytochemistry-supported FNAC only on US-suspect lymph node. Besides, the negative predictive value for our combined cytological and histological procedure was 94.7% (36/38) and the false negative rates in our series was 10.5% (2/19). Conclusions: The present preoperative protocol (US+FNAC and SLNB) is reliable for screening patients with lymph node metastases, thus avoiding sentinel lymph node biopsy in 18% (10/53) of MCC cases.