Prostate cancer is one of the most common cancers. About 1 in 8 men will be diagnosed with prostate cancer at some time during their lifetime, with most cases being discovered in men who are over 65. About 1 in 41 men will die from prostate cancer.
Current treatments for prostate cancer
Many patients with prostate cancer do not require treatment as it is a slow-growing type of cancer, and active surveillance is often adequate. Others are successfully treated. However, others will experience the cancer spreading to other organs (metastatic prostate cancer). Metastatic prostate cancer can be controlled with hormone therapy, but eventually this type of therapy may stop working. Anywhere from 10-50% of metastatic prostate cancers will evolve into a state known as metastatic castration-resistant prostate cancer (mCRPC) within 3 years. Despite recent advances in treatments for mCRPC, this disease is considered incurable and has a prognosis of only 2-3 years.
The cancer therapies generally considered for prostate cancer include radical prostatectomy, radiation therapy, chemotherapy, brachytherapy, and hormone therapy. Another type of therapy that has been used successfully in many types of cancer is monoclonal antibody therapy. Thus far, using monoclonal antibodies (MAbs) in treating prostate cancer has not been very successful. A type of MAb called “checkpoint inhibitors” has demonstrated deep and durable responses for a range of cancers but limited success in prostate cancer. This may be because prostate cancers are difficult for the immune system to “see” and are hard to access due to chemical and physical barriers around prostate tumors. However, a recent study has shown some promise in using MAb therapy for mCRPC patients.
What is monoclonal antibody (MAb) therapy?
An antibody is a specific protein that works with the immune system to help it recognize and destroy a specific foreign substance, which could be a specific virus or bacterium. A monoclonal antibody (MAb) is a protein that has been synthesized in a lab. Some MAbs are specifically designed to recognize and interact with specific cancer cells. Some work by marking the cells that the immune system should destroy. Others work by signaling T cells to get closer to the cancer cells by binding with both types of cells to help the T cells destroy the cancer cells.
MAb therapy is often called “immunotherapy.” It’s different from chemotherapy because, in general, it’s more targeted than chemotherapy can be–it recognizes specific types of invaders rather than using a scattershot approach. There are side effects of MAb therapy, including flu-like symptoms, allergic reactions, and even more life-threatening types of symptoms such as multiple organ failure. However, many types of cancer have been treated with MAbs with varying degrees of success.
MAb therapy and mCRCP
A recent study shows promise in using MAb therapy to treat mCRCP. In this study, two different MAbs, nivolumab and ipilimumab, were given together for four treatment cycles. Then, after a six-week break in treatment, nivolumab alone was used for up to a year. These two different MAbs target two different ways of stopping the spread of prostate cancer. This treatment showed the highest response rate yet for immunotherapy in mCRPC.
“These are the best results we’ve seen with this kind of immunotherapy for metastatic prostate cancer, although it is still early days. We believe the further study of nivolumab and ipilimumab in biomarker-selected patients with metastatic castration-resistant prostate cancer is warranted,” said Dr Mark Linch, Associate Professor (UCL Cancer Institute), Consultant Medical Oncologist (UCLH), and chief investigator of the trial.
What’s in the Future for MAbs and mCRCP?
Not all patients in the study managed to complete the treatment. Sometimes, this was a result of side effects from the treatment. The ongoing NEPTUNES trial is continuing to recruit men with mCRPC but using a better tolerated dosing schedule which will hopefully provide even more benefit to patients. This trial is also testing whether a subgroup of patients which have either (1) certain defects in the mechanism of DNA repair (making them more visible to the immune system) or (2) already have immune cells within the tumor may render them particularly sensitive to these treatments.
This type of cancer treatment is still very much in its trial stages. This study is valuable because the therapy shows exceptionally promising results. However, the therapy should certainly not be seen by patients as a replacement for successful treatments that are already being used for prostate cancer. Consult with your healthcare providers to determine which treatment is likely to get the best results in your particular situation.
However, continued testing of monoclonal antibody therapy as an additional treatment for prostate cancer can give hope to the many mCRCP patients whose cancers have stopped responding to hormone therapy.
References
- Key Statistics for Prostate Cancer
- Prostate Cancer Treatment
- Metastatic Castration-Resistant Prostate Cancer Previously Treated With Docetaxel-Based Chemotherapy: Treatment Patterns From the PROXIMA Prospective Registry
- Monoclonal Antibodies
- Checkpoint Inhibitors
- Combination immunotherapy for metastatic prostate cancer shows promise
