TYROSINASE, MELAN-A, AND KBA62 AS MARKERS FOR THE IMMUNOHISTOCHEMICALIDENTIFICATION OF METASTATIC AMELANOTIC MELANOMAS ON PARAFFIN SECTIONS

The authors retrospectively tested the potential value of paraffin-rea ctive monoclonal antibodies (A103 against melan-A, T311 against tyrosi nase) and antibody KBA62 as immunohistochemical markers for amelanotic metastatic melanomas, The study cases included 72 amelanotic metastas es of known cutaneous melanomas, 59 poorly differentiated carcinomas, 73 sarcomas of varying histogenesis, 4 Leydig cell tumors, 10 high-gra de lymphomas, and 6 plasmoblastic/anaplastic myelomas. The results wer e compared with immunostainings for S-100 protein and HMB-45. HMB-45, antimelan-A, and antityrosinase showed almost identical staining resul ts, with a sensitivity of 0.85 for HMB-45 and of 0.86 for both antimel an-A and for antityrosinase. HMB-45 and antityrosinase both had a spec ificity of 1.00; the specificity of antimelan-A was 0.95 as a result o f a positive reaction in three of three adrenocortical carcinomas and four of four Leydig cell tumors. KBA62 stainings resulted in a sensiti vity of 0.86 for melanomas. A positive immunoreactivity of KBA62 alone had a specificity of only 0.83, but in conjunction with anti-S-100 pr otein (sensitivity, 1.00; specificity, 0.87) and anticytokeratin 8/18/ 19 (CK), a KBA62+/S-100+/CK- immunophenotype identified all except one of the melanoma cases that were negative for the three melanocyte-spe cific markers with a specificity of 0.99. In conclusion, we found comp arable immunohistochemical sensitivities of HMB-45, antityrosinase, an d antimelan-A for a highly specific identification of approximately 85 % of amelanotic metastatic melanomas on paraffin sections. Melanomas t hat cc ere negative for all of these specific markers might be sensiti vely and specifically detected with anti-S-100 protein and KBA62.