BREAST CANCER THERAPEUTIC MEDICINE CONTAINING PYRIDAZINE DERIVATIVE AS ACTIVE INGREDIENT

PURPOSE:To provide a low toxic breast cancer therapeutic medicine containing a pyridazine derivative as an active ingredient and having an aromatase- inhibiting activity. CONSTITUTION:A breast cancer-treating agent contains a 3-(1H-imidazol-1- yl)pyridazine derivative of the formula (R is H, lower alkyl; R is benzyl, naphthylmethyl) or its salt as an active ingredient, can be prepared in the form of an oral administration agent or an injection agent, and is administered at a dose of approximately 0.01-200mg/kg once to several times a day for an adult. Since little in affections against other steroid-metabolizing enzyme systems and high in safety, the compound of the formula is useful for the therapy of hormone-dependent breast cancers as an aromatase-inhibiting agent having selectivity.