The difference between cancer genomics and genetics

As a breast oncologist, I often explain the difference between cancer genetics and cancer genomics to my patients particularly in the context of breast cancer.

DNA strand representing cancer genomics and cancer genetics.

Cancer genetics: The inherited risk

Cancer genetics focuses on the genes we inherit from our parents that can increase our risk of developing cancer. In breast oncology, this includes well-known genes like BRCA1 and BRCA2, which, when mutated, significantly raise the lifetime risk of breast and ovarian cancer. Other genes like PALB2, CHEK2, and ATM also contribute to hereditary breast cancer risk.

When we test for cancer genetics, we are looking at a person’s germline DNA - the genetic code that we are born with and can pass on to our children. This is why genetic counselling is crucial for patients with a strong family history of breast cancer, as identifying a hereditary mutation can guide both their treatment and preventive strategies for the patient and family members.

Cancer genomics: The tumour’s unique blueprint

Cancer genomics, on the other hand, looks at the DNA of the tumour itself, which is different from the DNA a person was born with. As cancer develops, cells acquire new mutations that drive their growth. In breast cancer, genomic tests like Oncotype DX or Endopredict analyse the activity of specific genes in a tumour to predict the risk of recurrence and help determine whether chemotherapy is necessary.

We also use genomic profiling to identify targetable mutations in metastatic (stage 4) breast cancer. For example, if a tumour has a mutation in the PIK3CA gene, we may use targeted therapies like alpelisib. If the tumour has high MSI (microsatellite instability) or a high TMB (tumour mutational burden), immunotherapy may be an option.

Application in breast cancer care

In short, cancer genetics tells us about a person’s inherited risk of developing breast cancer, while cancer genomics helps us understand the specific biology of an existing tumour, guiding treatment decisions. Both fields are crucial in modern breast oncology, allowing us to personalise care, from prevention to targeted therapy.