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