Abstract: The present invention provides pharmaceutical preparations for inhibiting in-vitro and in-vivo cancerous prostate, gastrointestinal and breast tumors. In one embodiment the pharmaceutical preparation includes human seminal prostatic inhibin which may be administered in an appropriate dosage form, dosage quantity and dosage regimen to a patient suffering from prostate cancer. In another embodiment the pharmaceutical preparation includes a mixture of human seminal prostatic inhibin and a anticancer drug which may be administered in an appropriate dosage form, dosage quantity and dosage regimen to a patient suffering from, for example gastrointestinal cancer. The anticancer drug of the latter mixture may be one selected from the group of drugs including mitomycin, idalubicin, cisplatin, 5-fluorouracil, methotrexate, adriamycin and daunomycin.