Breast cancer is the most common cancer in women worldwide. It is highly heterogeneous with distinct breast
cancer subtypes, posing challenges for diagnosis and treatment. There are four key molecular breast cancer
subtypes classified based on the expression of hormone and growth factor receptors.1
Luminal A subtype tumours are characterised by the expression of oestrogen receptor (ER+) and/or progesterone receptor (PR+) and the absence of human epidermal growth factor receptor (HER2-). Clinically, they are low grade, slow growing and have the best prognosis with less incidence of relapse and higher survival rate. Luminal B subtype tumours are of higher grade and have a worse prognosis than Luminal A tumours. They are ER+, can be PR+ or PR- negative and HER2- and are generally of intermediate/high histologic grade. These tumours may benefit from hormonal therapy along with chemotherapy. The HER2-positive subtype is characterised by high HER2 expression and is ER- and PR-. They grow faster than the luminal ones and prognosis has improved after the introduction of HER2-targeted therapies.
The triple-negative breast cancer (TNBC) subtype is characterised by the lack of expression of any of the above
receptors (ER-/PR-/HER2-). This is the most challenging breast cancer subtype as it is more aggressive and does not respond to hormonal therapies or HER2-targeted therapies. Treatment usually involves chemotherapy, and patients have a higher risk of early recurrence.
