To the Editor.
—Reverse transcription—polymerase chain reaction (RT-PCR) of messenger RNA of a specific gene may be a powerful tool to detect small numbers of circulating cancer cells in the blood. With respect to common solid cancers, cytokeratin or carcinoembryonic antigen genes have been used as target genes for RT-PCR. However, these genes are not specific to cancer cells. Recently, a number of genes that code for tumor antigens have been isolated. Some of these genes are expressed in various tumors, but are otherwise silent in normal adult tissue, except for testes. Thus, these antigens appear to be potential targets for molecular diagnosis by RT-PCR.One of these genes that codes for tumor antigens is the MAGE gene, the name of which is derived from melanoma antigen.2MAGE genes consist of 12 members and are localized on chromosome X.3 We previously studied the expression of 10 of the