PD-1 seems to be in the news a lot lately as a target for immunotherapy. Anti PD-1 therapies known as Pembrolizumab or Keytruda are able to block the programmed cell death protein that keeps the immune system from going after cancer cells. Before visiting the Hallwang clinic, they sent my tumor tissue to a lab and it was tested for EpCAM, MUC-1, PD-1 and several other tumor associated antigens that can be targeted with different therapies that are not available in Canada right now. Eventually, I believe these tests will be done at diagnosis the same way ER, PR and HER2 are tested today but it will take time.
Right now Keytruda is approved by the FDA (Food and Drug Administration) for malignant melanoma and non-small-cell lung cancer but is just starting to be used in clinical trials for breast cancer. Luckily those like me that don't qualify for the clinical trials or have 10 years to wait around for it to be approved as a first line therapy for breast cancer, have other options. At the Hallwang clinic they are able to use Keytruda to treat women that are PD-1 positive. Unfortunately it is costly but worth it in my opinion given that breast cancers positive for PD-1 carry a worse prognosis.
In many cancers, PD-1 is over expressed on tumor cells and tumor-infiltrating immune cells. When these join together, they form a biochemical "shield" protecting tumor cells from being destroyed by the immune system. Tumors can co-opt PD-1 to their own advantage to fly below the radar of the immune system. By using a blocking agent against PD-1, we can interrupt that shield protecting the tumor from immune destruction.
If you have been recently diagnosed, you may want to ask your doctor about whether they can test for PD-1. It has been suggested that anti PD-1 immunotherapies can be especially effective in triple negative breast cancer because ER-negative breast cancers typically have a higher density of tumor infiltrating lymphocytes than their ER-positive counterparts. TNBCs also have a higher mutational load compared with their ER-positive counterparts, and have been proposed as a mechanism for increased immunogenicity.
