NOVEL 7-SUBSTITUTED OXA- OR AZASTEROID COMPOUND

A 7-substituted oxa- or azasteroid compound represented by general formula (I), which has an excellent aromatase-inhibiting effect and is useful for preventing or treating diseases caused by estrogens, such as breast cancer, uterine cancer and prostatomegaly. This compound has an oxygen or nitrogen atom as the heteroatom at the position A of the ring D and the 7-position (substituent R ) of the skeleton is substituted by -S-R (wherein R represents hydrogen, lower alkyl which may be substituted by hydroxy, amino or lower alkoxycarbonyl, lower alkenyl, aralkyl, aryl which may be substituted by halogen, amino, di(lower alkyl)amino, lower alkoxy or lower alkyl, acyl, or lower alkoxycarbonyl), - S(O)m-R (wherein R represents lower alkyl; and m represents 1 or 2), or aralkyl.