Response of patients with advanced prostatic cancer to administration of somatostatin analog RC-160 (vapreotide) at the time of relapse.

Background: The aim of this study was to evaluate the effects of administration of the somatostatin analog RC-160 (vapreotide) at the time of relapse in patients with androgen independent prostate cancer.

Methods: Our study included 13 patients with biopsy-proven prostate cancer, stage D3. Eight patients had been treated with a depot formulation of the agonist D-Trp-6-LH-RH, with a median remission time of 68 (range 48-102 months). Five patients were initially treated by surgical orchiectomy, but relapsed after a median time of 33 months (range 17-91 months). A new remission period with a median duration of 10 months (range 2-29 months) was induced with Ketoconazole in the orchiectomy group. At the relapse time, all the patients received 1 mg of vapreotide t.i.d., by subcutaneous route, in addition to D-Trp-6-LH-RH, or Ketoconazole in the orchiectomy group.

Results: Eight of 13 patients demonstrated clinical improvement after 3 months of therapy with vapreotide, six showing a decrease in serum prostate specific antigen (PSA) from 234.5 +/- 308.5 to 68.2 +/- 60.5 ng/ml (mean decline 71 +/- 8%; P < 0.05). Two additional patients presented a fall in serum prostatic acid phosphatase (PAP). Responding patients showed a decrease in the bone pain score from 2.62 +/- 0.48 to 0.37 +/- 0.69 and an increase in the Karnofsky performance status from 72.3 +/- 4.21 to 83.6 +/- 23.2 (P < 0.05). In accord with the ECOG criteria, two patients had a complete response; four had partial response, and two had a stable response. Four patients did not respond and one was not evaluable. Two patients died in remission, one at 16 months due to myocardial infarction and the other at 24 months due to pneumonia. Three patients relapsed at 5, 17, and 19 months respectively. Three patients who have been followed-up for more than 3 years continued in remission (79, 45, and 45 months) respectively. Vapreotide was well tolerated, only three patients having transitory mild diarrhea.

Conclusions: Our results indicate that therapy with the somatostatin analog vapreotide at the time of relapse can induce objective clinical responses in some patients with prostate cancer who are refractory to androgen ablation induced by LH-RH analogs or orchiectomy.