Immunotherapy for breast cancer
Breast cancer is the commonest cancer affecting women and a major concern for women after menopause. Screening programs have led to a dramatic decrease in breast cancer mortality rates since most cancers discovered are surgically resectable with breast conservative surgery, but advanced cases are still present in developing countries and in some cases who don’t undergo regular screening.
The main modalities of breast cancer therapy are surgery, chemotherapy, radiotherapy, and hormonal therapy. In the recent past, breast cancer was considered a bad candidate for immunotherapy since it was thought to be immunologically “cold” which means that its cells do not have enough targetable receptors by immunotherapy. This claim has been refuted by recent clinical trials that explored the effectiveness of immunotherapy in advanced breast cancer especially triple-negative breast cancer -which is considered immune to hormonal therapy- and HER2 neu breast cancer.
When your doctor orders a breast biopsy following suspicion of breast cancer, it is done for 2 main reasons: the first is to confirm the diagnosis, and the second is to detect the “biological behavior” of the cancer. The biological behavior of cancer is the number and type of receptors on the surface of its cells. The main receptors found in cancer cells are estrogen receptors, progesterone receptors, HER2/neu, and ki-67. Breast cancer which proves to be rich in estrogen or progesterone receptors is ideal for hormonal therapy. Cancers with neither estrogen, progesterone nor her2 receptors are considered triple negative.
Monoclonal antibodies have been developed to target the her2 in her2-rich cancers. Available medications include Trastuzumab which is sold as a monoclonal antibody under the name Herceptin or as an antibody-drug complex under the names Enhertu and Kadcyla. It is only effective in breast cancers rich in her2 neu receptors and mostly ineffective in others. Other immunomodulatory therapies are also available including the checkpoint inhibitors Pembrolizumab and Atezolizumab. They are mainly used for advanced triple-negative breast cancer and breast cancer with certain mutations in genes called mismatch repair genes (MMRs).