Human mammary and thyroid tumors as well as peripheral blood cells of the same patients were examined for the amplification of oncogene fins and the expression of its product. Of the 7 mammary tumors analyzed, amplification of fms was observed in 6 (86%) mammary tumor DNAs, while no amplification was seen in 5 thyroid tumors and 7 peripheral blood cell DNAs tested. None of the mammary and thyroid tumors showed any rearrangement of the fms gene. Investigations of the expression of the product of fms in various human tumors were carried out following the method of immunohistochemical staining in which polyclonal antibody to the fms gene product was used. The incidence of the expression of fms gene product in the tumors of mammary and thyroid glands, prostate and ovary, the hormone-dependent organs, was 38-97%, whereas fms protein was found to be present only in 20 and 42% of the tumors from hormone-independent organs, the brain and the bladder. Expression of the fms gene product was not detectable in normal tissue surrounding the tumor tissue in any of the cases examined. These results suggest that the expression of the product of fms may be associated with the development of some tumors of hormone responsive organs, especially the breast and thus the fms gene product may be a valuable marker for human mammary tumors.

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