The use of immunocytochemical study in the cytologic diagnosis of melanoma: evaluation of three antibodies.

There are limited studies on the utility of immunostaining in cytologic specimens suspected of melanoma. In this study, we examined the performance of the most commonly used antibodies including monoclonal antibodies against Melan-A (A103), S-100, and HMB-45 antigens. Immunostains were performed on formalin-fixed, paraffin-embedded cell blocks prepared from 100 cytologic specimens. The specimens consisted of 57 melanomas and 43 nonmelanocytic neoplasms. Of 57 melanomas, 53 showed positive reaction to Melan-A antibody while 51 and 41 revealed positive immunostaining for S-100 and HMB-45, respectively. Of 43 nonmelanocytic neoplasms, 10, 4, and 8 specimens stained positive with an antibody against S-100, HMB-45, and Melan-A, respectively. However, the false-positive immunostaining for Melan-A was eliminated in seven of the eight specimens after applying the pretreatment with avidin/biotin blocking reagents. Overall, the highest sensitivity and negative predictive value (NPV) were achieved in Melan-A antibody (93 and 90%) compared with antibodies to S-100 (89 and 85%), and HMB-45 (72 and 71%). Initially, an intermediate specificity and positive predictive value (PPV) were obtained for Melan-A antibody (81 and 87%) that were greater than S-100 (77 and 84%), and lower than HMB-45 (91 and 91%). However, the aforementioned treatment with avidin/biotin blocking reagents improved both specificity (98%) and PPV (98%) for Melan-A antibody. In conclusion, by blocking endogenous biotin, Melan-A antibody offers the greatest performance. In terms of cost-effectiveness, we suggested that Melan-A antibody should be used as the first-line antibody for detecting melanoma in the cytologic specimens.