Immunoreactivity of A103, an antibody to Melan A, in canine steroid-producing tissues and their tumors

The monoclonal antibody A103 to the melanocytic differentiation antigen Mel an A stains human steroid-producing cells and their tumors. A total of 200 formalin-fixed, paraffin-embedded canine normal tissues and hyperplastic an d neoplastic lesions of the adrenal gland, testis, and ovary were immunohis tochemically tested for Melan A with antibody A103. Leydig cell tumors (23/ 23, 100%), Sertoli cell tumors (14/15, 93%), and adrenocortical adenomas (1 2/13, 92%) were consistently positive. Adrenocortical carcinomas (23/35, 65 %) and granulosa cell tumors (10/17, 59%) were less frequently positive. Al l pheochromocytomas, seminomas, and dysgerminomas were negative. The patter n of staining was cytoplasmic, but nuclear staining was also frequently see n in normal Leydig cells and their tumors. As in human tumors, immunohistoc hernistry for Melan A stains many canine steroid-producing tumors and can b e used to distinguish these tumors from those of nonstereidogenic cells.