From the Guidelines
Breast cancer is classified into several types based on molecular markers, including Hormone Receptor-positive, HER2-positive, and Triple-negative breast cancer, which guide treatment decisions and are essential for personalized treatment planning. The main types of breast cancer include:
- Hormone Receptor-positive (estrogen receptor and/or progesterone receptor positive), which accounts for about 70% of cases and responds to hormonal therapies like tamoxifen or aromatase inhibitors 1
- HER2-positive, which overexpresses the HER2 protein and is treated with targeted therapies such as trastuzumab (Herceptin) 1
- Triple-negative breast cancer, which lacks all three receptors and typically requires chemotherapy 1 Other less common types include:
- Inflammatory breast cancer, characterized by redness and swelling
- Lobular carcinoma, which begins in the milk-producing glands Important prognostic and predictive markers include:
- Ki-67 (indicating proliferation rate) 1
- Tumor infiltrating lymphocytes (reflecting immune response)
- Genomic assays like Oncotype DX that help determine recurrence risk and chemotherapy benefit 1 These markers are essential for personalized treatment planning, as they help oncologists select the most effective therapies while minimizing unnecessary treatments. Breast cancer typing is performed through immunohistochemistry on tissue samples obtained during biopsy or surgery, with additional genomic testing often performed to further refine treatment decisions 1.
From the FDA Drug Label
The safety and efficacy of trastuzumab in women receiving adjuvant chemotherapy for HER2 overexpressing breast cancer were evaluated in an integrated analysis of two randomized, open-label, clinical trials (Studies NSABP B31 and NCCTG N9831) Breast tumor specimens were required to show HER2 overexpression (3+ by IHC) or gene amplification (by FISH) In HERA, breast tumor specimens were required to show HER2 overexpression (3+ by IHC) or gene amplification (by FISH) as determined at a central laboratory In BCIRG006, breast tumor specimens were required to show HER2 gene amplification (FISH+ only) as determined at a central laboratory
The types of breast cancer that are relevant to trastuzumab treatment are those with HER2 overexpression or HER2 gene amplification, which can be determined by:
- IHC (Immunohistochemistry): 3+ staining
- FISH (Fluorescence In Situ Hybridization): gene amplification These markers are used to identify patients who may benefit from trastuzumab treatment 2
From the Research
Types of Breast Cancer
- Invasive ductal carcinoma (IDC) is a type of breast cancer that begins in the milk ducts and invades the surrounding tissue 3, 4.
- Invasive lobular carcinoma (ILC) is a type of breast cancer that begins in the lobules and invades the surrounding tissue 3, 4, 5.
- Mixed invasive ductal and lobular carcinoma (IDC-L) is a type of breast cancer that contains both IDC and ILC components 3, 4.
Breast Cancer Markers
- Hormone receptor (HR) status is a marker used to determine if a breast cancer is driven by hormones such as estrogen and progesterone 4, 6.
- HER2 status is a marker used to determine if a breast cancer has high levels of the HER2 protein, which can promote cancer growth 4.
- E-cadherin is a protein that helps cells stick together, and loss of E-cadherin is a characteristic of invasive lobular carcinoma 5, 6.
Prognosis and Treatment
- The prognosis of breast cancer varies depending on the type and molecular subtype of the cancer 3, 4.
- Treatment decisions should be based on the pathological type and molecular subtype of the cancer 4.
- Endocrine therapy is often used to treat invasive lobular carcinoma due to its low chemosensitivity and high estrogen receptor positivity 5.
- Genetic screening for CDH1 mutations is important for women with early-onset bilateral lobular breast cancer or a strong family history of breast cancer 6.