The use of prostate-specific antigen as a surrogate end point in the treatment of patients with hormone refractory prostate cancer

Response and palliation in a phase II trial of gemcitabine in hormone-refractory metastatic prostatic carcinoma. Swiss Group for Clinical Cancer Research (SAKK)

BACKGROUND

In a phase II trial, 43 patients with hormone-refractory prostate cancer were treated with gemcitabine at a dose of 1,200 mg/m2 over 2 hours (later decreased to 1,000 mg/m2 due to hematological toxicity) on days 1, 8 and 15 of a 28 day cycle.

PATIENTS AND METHODS

Inclusion criteria were proven tumor progression after hormonal treatment and increased PSA levels, a WHO PS < or = 2, adequate bone marrow reserve, liver and renal function and age < or =, 80 years. Response criteria were based on PSA levels (CR: normalization of PSA, PR: > 50% decrease). Quality of life (QL) was assessed with the EORTC QLQ-C30 on day 1 of each treatment cycle and on day 8 of the first cycle (range of scales 0-100). Physician-rated pain intensity and use of pain medication were assessed at the same timepoints.

RESULTS

Hematological toxicity of gemcitabine led to a dose-reduction in 48% of all cycles. Three of forty-three patients (RR = 7%) showed a PSA response: one CR and three PR with time to treatment failure of 8.7, 6.6 and > or = 9.3 months. Seven patients (16%) had stable disease (NC) for a median duration of 7.1 months (range 6.1-11.7 months). There was one case with objective regression of lymph node metastases. Patients reported a considerably impaired health status/QL (n = 41, median = 50) and severe fatigue (n = 41, median = 55.6) at baseline, with no change under treatment. Pain (QLQ-C30) was also severe at baseline (N=41, median=50) but was improved at the end of cycles 1 (n = 33, median change = -16.7, P = 0.0002), 2 (n = 19, median change = -33.3, P = 0.0006), 3 (n = 14, median change = -16.7, P = 0.06) and 4 (n = 9, median change = -33.3, P = 0.04). Patient-rated pain and use of analgesics as combined endpoint yielded palliation for at least 8 weeks in 14 patients (32%). Nine of these patients showed at least stable disease (CR/PR or NC by PSA level), five indicated a benefit in spite of progressive disease.

CONCLUSIONS

Gemcitabine in the dose and schedule indicated above has a significant beneficial impact on pain in patients with hormone-refractory prostatic carcinoma despite its limited activity in terms of PSA response and considerable, especially hematological, toxicity.

Prostate-specific antigen and other markers of therapeutic response

Several new agents and combinations demonstrate significant activity in the treatment of patients with hormone refractory prostate cancer. Prostate-specific antigen (PSA) is being used increasingly as the key marker of a therapeutic response in trials of new agents. This article reviews data that support this marker as a surrogate endpoint, and it discusses the issues around the appropriateness of PSA as an intermediate marker with evolving noncytotoxic agents. Other biomarkers of prostate cancer progression are not uniformly elevated in men with advanced disease; to date, they are of limited clinical use. This article also discusses the rationale and results of novel and alternative biomarkers of prostate cancer progression.