Breast cancer and high-grade serous ovarian cancer are leading causes of cancer-related death in women. For many families, these diagnoses are linked to inherited mutations, or mistakes, in the BRCA1 gene. This gene appears in every cell of the body and plays a critical role in repairing damaged DNA. Normally, cells carry two copies of the BRCA1 gene, so if one doesnโt function properly, the other can act as a backup. However, if additional mutations occur, this repair system can fail, allowing cancer to develop.
BRCA1-related cancers are aggressive and difficult to treat. They also share a puzzling feature compared with other tumours: they contain larger numbers of immune cells. This suggests the immune system recognizes the cancer and is gathering to destroy it โ yet something prevents these immune cells from attacking the tumour. As a result, despite the presence of immune cells, BRCA1-related tumours do not respond better to immunotherapies than other cancers.
This raises an important question: Are the immune cells in the tumour failing to attack, or has the immune system been altered so that it helps, rather than hinders, these cancers?