Sipuleucel-T in prostate cancer
To date, sipuleucel-T (a cancer vaccine) is the only treatment targeting the immune system to be approved for the treatment of prostate cancer in the United States. Sipuleucel-T treatment involves removing a patient’s white blood cells, teaching them how to target prostate cancer cells, and then re-infusing them back into the patients. This treatment approach has been shown to decrease the risk of death in patients with advanced metastatic castration resistant prostate cancer by 22%. Other cancer-targeting vaccines (including PROSTVAC) are being studied for patients with prostate cancer; however, they are not approved and are not available for patients in routine clinical use.
In terms of immune checkpoint inhibitors, only one is approved for patients with advanced prostate cancer: pembrolizumab was approved for patients with advanced tumors regardless of which organ they came from if the tumor showed evidence of high level of mutations (so-called high microsatellite instability [MSH-high]). This is seen in approximately 3% of patients with advanced prostate cancer.
After many promising studies in other cancers including melanoma (a type of skin cancer), lung cancer, kidney cancer, bladder cancer, and others, a number of studies were designed to test whether immune checkpoint inhibitors may be beneficial for patients with advanced prostate cancer. Some of these studies have looked at using immune checkpoint inhibitors alone (with ADT continuing) while others have looked at combinations with other approved prostate cancer medications (including novel hormonal treatments like enzalutamide or targeted therapies like PARP inhibitor) or with combinations of immune checkpoint inhibitors.
Unfortunately, to date, while early studies were promising, these have not shown a benefit to this treatment approach and, as a result, immunotherapy is not approved (apart from pembrolizumab in patients with MSI-high as discussed above) for most patients with advanced prostate cancer.