Precision Medicine in Breast Cancer

Precision medicine in breast cancer refers to using tumour biology, biomarkers, and in some cases inherited genetic information to guide treatment more specifically than a one-size-fits-all approach. It does not mean every patient receives a completely unique therapy, but it does mean that treatment decisions increasingly depend on the biologic profile of the cancer. ^[1][2][3][4]

What does precision medicine mean in this setting?

The core idea is that breast cancer is not one disease. Tumours differ in hormone-receptor status, HER2 expression, growth features, mutational patterns, stage, and behaviour. Precision medicine uses these differences to choose or avoid particular treatments. In practice, this often means that treatment is guided by pathology and biomarker testing rather than by tumour size alone. ^[1][2][4][5]

This is why some patients receive endocrine therapy, some anti-HER2 drugs, some chemotherapy, some combinations, and some additional genomic or molecular testing. The more relevant question is often not “What is the standard treatment for breast cancer?” but “What is the standard treatment for this subtype of breast cancer in this clinical setting?” ^[2][3][5]

The most commonly used biomarkers in breast cancer

The most established biomarkers include oestrogen receptor (ER), progesterone receptor (PR), and HER2. These markers help determine whether endocrine therapy or HER2-directed therapy may be useful. Proliferation markers such as Ki-67 may also contribute in some settings, though interpretation and weight can vary. In selected early-stage cases, genomic assays may help estimate recurrence risk and whether chemotherapy is likely to add meaningful benefit. ^[1][2][4][6]

Genetic tests and inherited risk such as BRCA

Inherited testing is a different question from tumour biomarker testing, but it can be equally important in selected patients. BRCA1, BRCA2, and other hereditary cancer genes may influence risk assessment, surgery planning, family counselling, and, in some situations, systemic treatment options. Not every patient needs the same inherited test panel, and the decision depends on age, family history, tumour characteristics, ancestry, and guideline criteria. ^[2][3][5][7]

Targeted and personalised treatment options

Targeted treatment in breast cancer may include endocrine therapy, HER2-targeted therapy, CDK4/6 inhibitors, PARP inhibitors in relevant inherited-mutation settings, antibody-drug conjugates, and other biologically matched options depending on stage and subtype. That said, personalised treatment does not automatically eliminate the need for chemotherapy. Sometimes precision medicine refines the use of chemotherapy; sometimes it helps identify who can avoid it; sometimes it adds new targeted options on top of it. ^{[1][2][4][6][8]}

Differences between early-stage and metastatic disease

Precision medicine does not look exactly the same in early-stage disease and metastatic disease. In earlier stages, the focus may be on reducing recurrence risk and avoiding overtreatment. In metastatic disease, repeated testing or broader molecular profiling may become more relevant if it opens access to later-line targeted therapies or trials. The treatment question shifts from “How do we minimise recurrence?” to “How do we control disease over time with the most appropriate biologic strategy?” ^[2][3][5][8]

Limits, access, and why specialist review matters

Precision medicine is powerful, but it has limits. Not every abnormality has an available targeted treatment. Test quality, sample adequacy, timing, cost, and access can influence what is realistically possible. Around the world, inequality in access remains a major issue. A treatment option that exists scientifically may not be available locally or may not be appropriate in that patient’s exact stage of disease. ^[1][3][7]

For that reason, specialist review and clear treatment discussion matter. Patients often benefit from understanding which tests are standard, which are optional, and which results actually change management. Precision medicine helps most when it sharpens a real clinical decision rather than adding testing without a practical consequence. ^[2][4][8]