Melanoma-inhibiting activity (MIA) mRNA is not exclusively transcribed in melanoma cells: low levels of MIA mRNA are present in various cell types and in peripheral blood

The detection of minimal amounts of melanoma cells by tyrosinase reverse tr anscription polymerase chain reaction (RT-PCR) is seriously hampered by fal se negative reports in blood of melanoma patients with disseminated melanom a. Therefore, additional assays which make use of multiple melanoma markers are needed. It has been shown that introduction of multiple markers increa ses the sensitivity of detection. Melanoma inhibitory activity (MIA) is one such melanoma-specific candidate gene. To test the specificity of MIA PCR, we performed 30 and 60 cycles of PCR with two different sets of MIA specif ic primers on 19 melanoma and 16 non-melanoma cell lines. MIA mRNA was dete cted in 16 out of 19 melanoma cell lines and in seven out of 16 non-melanom a cell lines after 30 cycles of PCR. However, MIA mRNA could be detected in all cell lines after 60 cycles of PCR. Also, in 14 out of 14 blood samples of melanoma patients, five out of six blood samples of non-melanoma patien ts and in seven out of seven blood samples of healthy volunteers, MIA mRNA was detected after 60 cycles of PCR, whereas no MIA PCR product could be de tected in any of the blood samples after 30 cycles of PCR. We conclude that low levels of MIA transcripts are present in various normal and neoplastic cell types. Therefore, MIA is not a suitable marker gene to facilitate the detection of minimal amounts of melanoma cells in blood or in target organ s of the metastatic process. (C) 1999 Cancer Research Campaign.