Expression of melanoma inhibitory activity in melanoma and nonmelanoma tissue specimens.

Melanoma inhibitory activity (MIA) is a small soluble protein secreted by malignant melanoma cells and chondrocytes. Prior studies suggested that MIA expression was relatively tissue-specific, making it a potentially useful marker for melanoma. The current investigations sought to more clearly define the range of tumor/tissue-types where MIA is expressed, compared with expression of 4 other potential melanoma marker genes (tyrosinase melanoma antigen recognized by T cells [MART-1/MelanA], gp100, and melanoma growth-stimulatory activity [MGSA/Gro alpha]). Expression of these genes was assayed by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry in 23 melanoma tumor specimens and in 25 additional nonmelanoma or nonmalignant specimens. MIA, tyrosinase, and MGSA were expressed in most melanoma specimens. Specificity was highest for MART-1, followed by MIA and tyrosinase. Increasing the number of cycles of amplification from 35 to 40 increased sensitivity but decreased specificity of most markers, though MIA was relatively robust. MIA mRNA was also detected in carcinomas of the colon, ovary, kidney, and head/neck, as well as in normal laryngeal epithelium. Although MIA discriminated melanoma from nonmelanoma at least as well as tyrosinase, no single mRNA marker had accuracy greater than 71%, raising potential concern about application of these particular mRNA markers to the minimal disease setting. HUM PATHOL 31:1381-1388.