90K (Mac-2 BP) is a tumor-associated protein belonging to the scavenger receptor cysteine-rich domain superfamily that is implicated in immune defense. It is reported that 90K influences on the prognosis of various cancers including breast cancer. We examined to explain that 90K is associated with proliferation and metastasis in prostate cancer. The impact of 90K was analyzed by combining cell cultures, in vitro invasion assay, cell proliferation assay and luciferase assay. Secreted 90K suppressed prostate cancer cell proliferation and invasion via a repression of AP-1 activity. But, the impact of 90K is masked through binding with galectin-3. The data suggest a strategy of strengthening the impact of 90K with knockdown of galectin-3 as a therapeutic approach to prostate cancer progression.