e16609 Background: 30% of pts with localized PC will have a biochemical relapse post local tx. Their optimal tx remains elusive. While androgen deprivation therapy is effective in reducing PSA level, its long-term benefit remain undefined, and it is associated with significant toxicities. Thus, evaluation of new non-toxic compounds in this pt population is warranted. P-MCP is a competitive inhibitor of galectin-3, a carbohydrate-binding protein, known to be involved in cancer pathogenesis. Pre-clinical data suggest that P-MCP is active in PC, and in two previous smaller clinical trials in biochemically relapsed prostate cancer (BRPC) pts, a PSA response/stabilization rate of 57%-75% was noted. In the present study, we aimed to evaluate the safety and PSA dynamics of P-MCP tx in BRPC pts. Methods: non-castrate non-metastatic BRPC pts were enrolled in a prospective phase 2 study of oral P-MCP tx, at 4.8 grams X 3/day for 6 months (mos). Eligible pts had 3 consecutive rise of PSA, without any tx in the previous 3 mos, a normal level of serum testosterone, and negative scans. The primary outcome was the rate of pts without disease progression (DP) (clinically, biochemically with stabilization/decrease of PSA or improvement of PSA doubling time = PSADT, and radiologically) at 6 mos. A Sample size of ≥ 50 pts provided 85% power to assess a decrease in DP rate from 80% (natural history) to 40% (P-MCP tx) at 6 mos. Pts that did not progress at 6 mos, were treated for subsequent 12 mos (secondary outcome of long term effect). Herein we report the results of the primary outcome analysis. Results: 53 pts were enrolled. Median age was 74 years. Tx of the primary tumor consisted of surgery in 13% (n = 7), radiation in 60% (n = 32), and both in 26% (n = 14). No pt had tx related grade 3/4 toxicity. One pt withdrew his consent after 1 mos. At present, 46 pts completed 6 mos of tx, and were analyzed for the primary outcome. Among them, 20% (n = 9) had grade 1 toxicity (all gas and bloating ). The primary outcome was met in 76% (n = 35), that did not progress at 6 mos of tx. Of these, 59% (n = 27) had a stabilization/decrease of PSA, 70% (n = 32) had an improvement (increase) of PSADT, and all had no metastases on scans at 6 mos. DP at 6 mos was noted in 24% (n = 11: PSA only in 20%, n = 9; PSA and scans in 4%, n = 2). Full cohort data (additional 6 pts that will complete 6 mos of tx) will be available by June 2019. Conclusions: The present study suggests the safety and potential benefit of P-MCP tx on progression of BRPC. Clinical trial information: NCT01681823.