The optimal therapy for patients with non-metastatic biochemically relapsed prostate cancer (BRPC-M0) after local therapy is elusive. Thus, the evaluation of new non-toxic compounds in BRPC-M0 patients is warranted. PectaSol® modified citrus pectin (P-MCP) is a food supplement generally recognized as safe (GRAS) by the Food and Drug Administration (FDA) and is a competitive inhibitor of galectin-3 protein, involved in cancer pathogenesis. P-MCP treatment of BRPC-M0 patients for 6 months led to a 75% prostate-specific antigen doubling time (PSADT) improvement. To determine the longer-term effects of P-MCP we investigated an additional 12 months of treatment (phase II) with oral P-MCP at 4.8 grams X 3/day in patients with no disease progression in the previous 6 months. Of the 46 patients that entered the second phase, 7 patients withdrew consent and continued therapy independently, and 39 received another 12 months of therapy. After a total of 18 months P-MCP treatment, 62% (n=24) had a decreased/stable PSA, 90% (n=35) had improved PSADT, and 85% (n=33) had a durable long-term response, with a decreased/stable PSA, and/or improvement of PSADT, and negative scans. No patient had grade 3/4 toxicity. In conclusion, P-MCP may have long term durable efficacy, and is safe, in BRPC-M0.