BACKGROUND: Insulin-like growth factor (IGF) mediated signaling has been implicated in the growth of many tumor types including prostate cancer, and it is hypothesized that lowering circulating IGF levels in men with castration resistant prostate cancer (CRPC) will slow tumor growth. In this study, the efficacy of depot octreotide acetate was prospectively evaluated in patients with CRPC.
METHODS: Eligible patients had progressive non-metastatic CRPC. Octreotide acetate 30 mg was administered intramuscularly every 28 days. Changes in PSA, IGF-1, IGF-2, IGF binding protein-1 (IGFBP-1), and IGFBP-3 were evaluated over time.
RESULTS: Accrual was stopped early after a pre-planned interim analysis showed no prostate specific antigen (PSA) declines after 3 cycles of treatment among the first 13 patients enrolled. Median baseline PSA and IGF-1 measurements were 36.2 ng/ml and 162.6 ng/ml, respectively, and median time on treatment was 13 weeks. Radiographic progression occurred in 7 patients, PSA-only progression occurred in 5 patients, and 1 patient was taken off the study due to a grade 3 drug interaction. After 3 cycles of treatment IGF-1 significantly declined with a median -34.5% (P = 0.01) and IGFBP-1 significantly increased with a median 76.3% (P = 0.046). IGF-2 and IGFBP-3 were not significantly changed from baseline.
CONCLUSIONS: Octreotide acetate significantly lowers IGF-1 and raises IGFBP-1 levels in patients with non-metastatic CRPC, but does not result in sustained declines in PSA. While treatment with single-agent octreotide may not be warranted, its inclusion in combination regimens directly targeting the IGF-1 receptor on tumor cells may be of interest.