Heterogeneous expression of MAGE-A genes in occult disseminated tumor cells: a novel multimarker reverse transcription-polymerase chain reaction for diagnosis of micrometastatic disease.

Systemically disseminated tumor cells have become the subject of intensive research as the presumed seminal precursors of later distant metastasis. We describe here a novel sensitive multimarker nested reverse transcription (RT)-PCR capable of detecting the individual expression of human MAGE-A genes MAGE-1, -2, -3/6, -4, and -12 by rare, disseminated tumor cells in bone marrow and blood of patients with many different types of cancer. We analyzed bone marrow aspirates from 106 patients with breast, lung, colorectal, and prostate cancer and with different sarcomas. Heterogeneous expression of the different MAGE genes was found frequently in all those kinds of malignancies, in sharp contrast to 30 bone marrow and 20 blood samples from healthy donors, which were completely MAGE negative. Expression of at least one MAGE gene in bone marrow was more frequent than cytokeratin-positive tumor cells detected by immunocytochemistry, although the results of both tests overlapped considerably. In 30 patients with clinically localized prostate cancer, analysis by the multimarker MAGE RT-PCR of bilateral bone marrow aspirates from the right and left iliac crest revealed a positivity rate of 60%, which was twice as high as that obtained with either an established prostate-specific antigen RT-PCR or by cytokeratin-based immunocytochemistry. Analysis of primary prostate cancer revealed MAGE expression patterns considerably concordant with those found in the corresponding bone marrow aspirates. Prostate cancer patients carrying an exceptionally high risk of metastatic relapse, as defined by clinical prognostic factors, were significantly more often MAGE positive than patients with a distinctly lower risk (P = 0.02, Fisher's exact test). More frequent MAGE expression in the peripheral blood of patients with metastatic prostate cancer compared with those with clinically localized disease added further evidence for the prognostic impact of the multimarker MAGE RT-PCR. Moreover, MAGE-positive bone marrow samples from a small group of seven sarcoma patients demonstrated the relevance of our multimarker RT-PCR in nonepithelial tumors. Because MAGE antigens can induce autologous cytolytic T lymphocytes in vivo, the determination of individual MAGE expression patterns in cancer patients may furthermore identify candidate vaccine targets for adjuvant immunotherapy.