A method is provided for treating hormone-regulated tumors (for example, breast and prostatic tumors) in mammals, including humans, by administration of an antisense ODN which is complementary to a portion of the gene encoding IGFBP-5. Using the Shionogi tumor model in vitro and in vivo, the administration of such an ODN was shown to reduce proliferation of tumor cells, and also to delay the progression to androgen independence. Thus, treatment of prostate cancer in mammals, including humans, and delay of the progression of prostate tumors to androgen independence is accomplished by administering to the mammal a therapeutically effective amount of an antisense oligodeoxynucleotide which is complementary to a portion of the nucleic acid sequence encoding IGFBP-5 and which hybridizes with such a sequence to inhibit expression of IGFBP-5. Specific antisense ODN's which are suitable for use in the method are GACCACGCTGATCACCAT (Seq. ID. No. 1), which is derived from the murine gene sequence, and CGCCGTGAGCAACACCAT (Seq. ID. No. 3) and AGGTCATGCACCAGCCGC (Seq. ID No. 4), which are derived from the human gene sequence.