Breast cancer is a heterogeneous disease, meaning it can be classified into different types based on various factors such as the presence or absence of certain receptors, the expression of specific genes, and the microscopic appearance of the tumor cells. The main types of breast cancer include:
Ductal Carcinoma In Situ (DCIS): DCIS is a non-invasive form of breast cancer where abnormal cells are found in the lining of a breast duct but have not spread outside the duct to nearby tissue. It is considered a pre-invasive stage of breast cancer and is often detected through mammography screening.
Invasive Ductal Carcinoma (IDC): IDC is the most common type of invasive breast cancer, accounting for about 70-80% of cases. It begins in the milk ducts of the breast and can spread to nearby tissues if not treated. IDC may present as a lump or mass in the breast and can sometimes cause changes in the breast’s appearance or skin texture.
Invasive Lobular Carcinoma (ILC): ILC is the second most common type of invasive breast cancer, accounting for about 10-15% of cases. It begins in the milk-producing glands (lobules) of the breast and can spread to surrounding tissues. ILC may not always form a distinct lump and can be more difficult to detect on imaging tests like mammograms.
Mixed Ductal and Lobular Carcinoma: Some breast cancers may have features of both invasive ductal carcinoma and invasive lobular carcinoma, referred to as mixed ductal and lobular carcinoma.
Triple-Negative Breast Cancer (TNBC): TNBC refers to breast cancers that lack estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression. TNBC accounts for about 10-15% of breast cancer cases and tends to be more aggressive than other types. It often requires different treatment approaches.
Hormone Receptor-Positive (HR+) Breast Cancer: HR+ breast cancers express estrogen receptor (ER) and/or progesterone receptor (PR) but do not overexpress HER2. They account for the majority of breast cancer cases and are often treated with hormone therapy targeting ER and/or PR.
HER2-Positive Breast Cancer: HER2-positive breast cancers overexpress the human epidermal growth factor receptor 2 (HER2) protein. HER2-positive breast cancers tend to grow more rapidly and are often treated with targeted therapies that inhibit HER2 signaling.