ASCO GU 2018: Immunotherapy for Biochemically Recurrent Prostate Cancer

San Francisco, CA ( Annually about 30-50,000 men are diagnosed with biochemically recurrent prostate cancer (BCRpc), defined by a rising PSA after radical prostatectomy (RP) or definitive radiation therapy (RT) with negative conventional imaging (CT and bone scan). Standard available treatments include salvage therapies, androgen deprivation or surveillance. The role of immunotherapy in this setting is undefined.

This study evaluated PROSTVAC, a pox-viral based therapeutic cancer vaccine targeting PSA, in BCRpc. Key eligibility criteria included PSA > 0.8 ng/ml after RP or > 2.0 ng/ml after RT with a maximum PSA of 30 ng/ml, PSA doubling time (DT): 5-15 months; testosterone > 100, and negative CT and bone scan. Patients (pts) were randomized to vaccine for 6 months or 6 months surveillance followed by 6 months of vaccine. In a post hoc analysis delayed PSA declines were characterized as a confirmed PSA decline after an intra-study apex PSA (ISAP) defined by a peak PSA affirmed by a contiguous PSA within 10% (to exclude lab variations). The authors planned the enrollment of 80 pts at the NCI, Dana-Farber Cancer Institute and Memorial Sloan Kettering Cancer Center.

Of the 26 pts enrolled thus far, 22 have been followed for more than 9 months after they received the vaccine. On-study median values were age 66.8 years (54-78), PSA 2.67 ng/ml (0.83-28.5), and PSA DT 7.5 months (5.1-14.9). 8 pts (38%) had delayed PSA declines after ISAP (-12% to -99%). Of the 13 pts on surveillance for 6 months, only one pt had a similar decline lasting only 56 days.

Preliminary data from this study suggests that PROSTVAC vaccine may be associated with a delayed, but sustained PSA decline in BCRpc patients, which are rarely seen in surveillance alone. As additional data will be acquired from this study, this data provide a rationale to develop immunotherapy combinations in BCRpc. Clinical trial information: NCT02649439

Presented by: Ravi Amrit Madan

Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, Twitter:@GoldbergHanan at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA