Breast Cancer Subtypes
In many ways, every breast cancer journey begins with the pathology report. It provides the foundation for understanding the type of breast cancer, how it is likely to behave, and which treatments are most appropriate. This information is then combined with imaging findings and other clinical factors to develop a personalised treatment plan. As a specialist oncoplastic and reconstructive breast surgeon in Melbourne, one of the most important conversations I have with patients is discussing the results of their breast biopsy. While this initial discussion can feel overwhelming, having a better understanding of the pathology empowers patients to ask informed questions and actively participate in decisions about their care.
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Breast Cancer Subtypes Based on Histology
Breast cancer is an abnormal growth of cells within the breast. Most commonly it arises from the cells lining the milk ducts (ductal cancer) or milk producing lobules (lobular cancer). However, it can arise from any cells within the breast.
If the cancer cells stay within the duct/lobular system it is called in situ cancer; either ductal carcinoma in situ (DCIS) or lobular carcinoma in situ or (LCIS). If the cancer cells pass through the duct/lobular system into the surrounding breast tissue, it is called invasive breast cancer (invasive ductal or invasive lobular carcinoma).
Breast Cancer Subtypes Based on Receptor Status
A more contemporary and useful way of discussing breast cancer subtypes is using the receptor status on the pathologic analysis. Breast cancer cells may or may not express oestrogen and/or progesterone (so called hormone positive or negative). The other receptor is called Her2 which if overexpressed can be responsible for rapid growth of cancer cells. Based on these three receptors, breast cancer can be divided into the following 4 subtypes:
Hormone receptor + / Her2 -
Hormone receptor + / Her2 +
Hormone receptor - / Her2 +
Triple negative (Oestrogen, progesterone, and Her2 negative)
The importance of this classification is its implication in the treatment of breast cancer. For example, a patient with hormone positive breast cancer will benefit from anti-hormone therapy. Similarly, a patient with Her2 + breast cancer will benefit from specific anti-Her2 medications which is administered along with chemotherapy. On the other hand, patients with triple negative breast cancer most often will need chemotherapy as none of the other systemic therapies are going to be effective.
Frequently Asked Questions
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A breast cancer subtype describes the biological characteristics of a breast cancer based on whether the cancer cells express hormone receptors (oestrogen and/or progesterone receptors) and the HER2 protein. The subtype is one of the most important factors in determining which treatments are most likely to be effective.
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Your breast cancer subtype is determined by analysing tissue obtained during a breast biopsy or surgery. The pathology laboratory performs specialised tests called immunohistochemistry (IHC) to determine whether the cancer cells express oestrogen receptors (ER), progesterone receptors (PR), and HER2. In some cases, an additional test called FISH (fluorescence in situ hybridisation) may be required to clarify the HER2 result.
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Although uncommon, breast cancer receptor status can occasionally change, particularly if the cancer recurs or spreads to another part of the body. For this reason, a repeat biopsy is often recommended if recurrent or metastatic disease develops to ensure treatment is based on the current biology of the cancer.
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In general, hormone receptor-positive, HER2-negative breast cancers tend to have the most favourable prognosis because they often grow more slowly and respond well to endocrine (hormone-blocking) therapy. However, the outlook for every patient depends on many other factors, including tumour size, lymph node involvement, tumour grade, stage at diagnosis, and response to treatment.
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Before the development of targeted therapies, HER2-positive breast cancer was associated with a poorer prognosis. Today, highly effective HER2-targeted treatments have dramatically improved outcomes, making many HER2-positive breast cancers highly treatable with excellent long-term survival.
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Triple-negative breast cancer often grows more quickly than other subtypes and cannot be treated with hormone therapy or HER2-targeted therapy. However, it is frequently very responsive to chemotherapy, particularly when treated before surgery (neoadjuvant chemotherapy). Many patients achieve an excellent outcome, especially when a complete pathological response is obtained.
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Yes. Breast cancer subtype is one of the most important factors influencing whether chemotherapy is recommended. Hormone receptor-positive cancers may sometimes avoid chemotherapy depending on genomic testing and other tumour characteristics, whereas HER2-positive and triple-negative breast cancers more commonly benefit from chemotherapy as part of their treatment.
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Your pathology report provides far more information than simply confirming the diagnosis of breast cancer. It describes the cancer subtype, tumour grade, size, lymphovascular invasion, receptor status, and other features that help your multidisciplinary team develop a personalised treatment plan. In many ways, every treatment decision begins with the pathology report.