We present the case of a man with metastatic, castration resistant prostate cancer who had a complete PSA response after 2 1/2 doses of ipilimumab. His treatment course was complicated by diarrhea and autoimmune hepatitis, both of which resolved within four months. Sera and biopsy specimens were accessed and sera from pretreatment and day 113 were analyzed. Augmented antibody responses were detected against 11 potential tumor antigens, with responses ranging from 5 to 20 fold in day 113 sera compared to baseline. Genes that were targets of a strong antibody response (arbitrarily set at 10 fold or greater increase) were analyzed by RT-PCR for expression in the tumor biopsy cDNA. Of the top 5 genes only HIBCH could be identified in the amplified tumor biopsy cDNA. Using an antibody to HIBCH, immunohistochemical analysis documented strong expression of the protein. Together these data suggest that an augmented antibody response to HIBCH, an antigen that was expressed by the patient's prostate cancer, could have contributed to the clinical response. After 16 months of PSA stability, he discontinued his androgen suppression therapy. With the return of his testosterone, his PSA rose slightly, likely originating from his intact prostate. He has been disease-free for the past six years without any additional therapy.
- Received October 30, 2013.
- Revision received January 3, 2014.
- Accepted January 20, 2014.
- Copyright © 2014, American Association for Cancer Research.