Findings from a real-world study of sipuleucel-T (Provenge) immunotherapy may help define expected overall survival rates in men who receive the treatment for asymptomatic/minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC).

Using the large PROVENGE Registry for the PROCEED (Observation, Collection, and Evaluation of Experience Data) trial, Celestia S. Higano, MD, of the Seattle Cancer Care Alliance, the University of Washington, and Fred Hutchinson Cancer Research Center in Seattle, and colleagues evaluated outcomes of sipuleucel-T treatment among 1976 men who had a median follow-up of 46.6 months. The median overall survival (OS) time was 30.7 months. The median time from the first infusion of sipuleucel-T to death from prostate cancer was 42.7 months. The incidence of serious adverse events related to sipuleucel-T was 3.9%.

“PROCEED provides contemporary survival data for sipuleucel-T–treated men in a real-world setting of new life-prolonging agents, which will be useful in discussing treatment options with patients and in powering future trials with sipuleucel-T,” Dr Higano’s team concluded in a paper published in Cancer. “The safety and tolerability of sipuleucel-T in PROCEED were consistent with previous findings.”

Steven Canfield, MD, Chief of Urology at McGovern Medical School of the University of Texas Health Science Center and Director of Urology at Memorial Hermann-Texas Medical Center in Houston, said the new findings are provocative because sipuleucel-T use has been controversial. “To have a real-world study like this with such a huge number of patients is really nice for practitioners and for those who believe it works and use it,” Dr Canfield told Renal & Urology News. “The adverse effect profile was very good and so that was comforting to see.”

Oncologist Zachery Reichert, MD, PhD, of the University Michigan in Ann Arbor, said the study is particularly important because of the large number of patients enrolled and the 3-year safety follow-up. “It shows sipuleucel-T remains safe,” Dr Reichert said. “The main limitation [of the study] is its registry design, thus lack of control group and no standardized decision matrix for when subsequent therapies are started. I was surprised to see the number of patients (32.5%) who did not receive further therapy 1 year after sipuleucel-T administration, as most of them had not received any prior life-prolonging therapies.”

The new findings reinforce the observed clinical heterogeneity of prostate cancer, making development of predictive biomarkers critical, he said.

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Urologic oncologist Marc Dall’Era, MD, of the University of California Davis, said one of the strengths of this study is that it broadly shows the practice patterns and usage of sipuleucel-T since its introduction in 2011. The study confirms the overall good tolerability of the treatment across clinical characteristics. The median OS rates reported in PROCEED are substantially better than noted in the original IMPACT (Immunotherapy for Prostate Adenocarcinoma Treatment) sipuleucel-T randomized trial. This is not surprising, however, as the current study includes lower-risk men, and the majority of the patients received multiple life prolonging agents, Dr Dall’Era said. “Unfortunately, these findings do not provide insight into better trial design or novel therapeutic targets. It should, however, be viewed as a model for studying real-world experiences with novel therapeutic agents after FDA approved, which rarely happens in contemporary oncology,” he said.

Some men received prior docetaxel, abiraterone, or enzalutamide, and most had bone-dominant metastases with or without lymph node involvement. PROCEED enrolled a higher proportion of African American patients than the IMPACT trial (11.6% vs 6.7%), “and this is notable because this population is often underrepresented in clinical trials,” Dr Higano and her collaborators wrote.

A post hoc analysis showed that the median OS was longer for men in the lowest baseline PSA quartile (5.27 ng/mL or less). During PROCEED, 1,483 men (78.0%) received 1 or more OS-prolonging anticancer interventions (ACIs), and 48.3% received 2 or more lines of treatment after sipuleucel-T. The most commonly used OS-prolonging ACIs after sipuleucel-T treatment were abiraterone (54.5%), enzalutamide (43.7%), and docetaxel (38.9%). A total of 419 men received sipuleucel-T as the only OS-prolonging treatment.

Reference

Higano CS, Armstrong AJ, Sartor AO, et al. Real-world outcomes of sipuleucel-T treatment in PROCEED, a prospective registry of men with metastatic castration-resistant prostate cancer [published online September 4, 2019]. Cancer. doi: 10.1002/cncr.32445