Lower PSA linked to greater survival with sipuleucel-T in prostate cancer
medwireNews: Sipuleucel-T treatment may be of the most benefit to patients with metastatic castration-resistant prostate cancer (mCRPC) who have low prostate specific antigen (PSA) levels, say US researchers.
An analysis of findings from the phase III Immunotherapy for Prostate Adenocarcinoma Treatment (IMPACT) trial showed that the magnitude of treatment benefit was greatest in patients with better baseline prognostic factors, particularly those with lower baseline PSA values.
"These findings provide a rationale for immunotherapy as an early step in sequencing treatment algorithms for mCRPC and also suggest a greater benefit when immunotherapy is used earlier in the treatment paradigm," say Philip Kantoff (Harvard Medical School, Boston, Massachusetts) and team.
For the randomized, double-blind, controlled multicenter trial, which included 512 men with mCRPC, subgroup analyses were performed based on prognostic variables that have previously been used to predict survival in patients with mCRPC. These included serum lactate dehydrogenase, PSA, serum alkaline phosphatase, Gleason score, Eastern Cooperative Oncology Group performance status, hemoglobin, and the presence of visceral disease.
Multivariate analysis showed that of all the factors assessed, PSA was the strongest baseline prognostic factor for survival among the men, report Kantoff et al.
Furthermore, there was a significantly greater treatment effect with decreasing baseline PSA level such that those in the lowest PSA quartile (<22.1 ng/mL) had a 49% reduction in risk for death compared with patients in the control group, while those in the highest quartile had a 16% reduction in risk.
Furthermore, those in the lowest versus highest baseline PSA quartile had an estimated median survival time of 41.3 versus 18.4 months in the sipuleucel-T group and 28.3 versus 15.6 months in the control group. And the estimated 3-year survival in the lowest PSA quartile was 62.2% in the sipuleucel-T group, compared with 41.6% in the control group, a significant relative increase of 50%.
"The overall finding of a greater sipuleucel-T treatment effect in patients with generally more favorable prognostic features is consistent with the proposed mechanism of action of sipuleucel-T," remark the researchers. "Patients with a lower cancer burden tend to experience less immunosuppression systemically and in the tumor microenvironment."
"Therefore, patients earlier in the natural history of the disease would be anticipated to have a more robust and effective immunologic response to sipuleucel-T treatment," note Kantoff and colleagues.
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By Sally Robertson, medwirenews Reporter