Breast Cancer Awareness Month: Different Types of Breast Cancer

By: Ava Bermudez

Breast cancer is a type of cancer that develops in the breast tissue, and it begins as a growth of cells in the breast tissue and it has a death toll of 2.3%, however this data varies based on the stage of cancer, the type of breast cancer, the age at diagnosis, and the race of the patient. Breast cancer can be an aggressive form of cancer, and some forms can be fatal while others can be expected to die with chemotherapy. But the main question a lot of women have is, what type of cancer do I have?

Breast cancer is not a single disease, but rather a collection of different types, each defined by where the cancer starts in the breast tissue, the cancer's cellular characteristics and the cancer's molecule markers. It is crucial for women around the globe to understand the differences in breast cancer types because it heavily influences prognosis and treatment decisions. Anatomically, most breast cancers originate in the breast ducts or lobules. The two most common types of invasive breast cancers are invasive ductal carcinoma (IDC), and invasive lobular carcinoma (ILC). IDC begins in the milk ducts and then invades the surrounding breast tissue. IDC accounts for roughly 70-80% of invasive breast cancers, and it tends to form a distinct lump. ILC starts in the milk-producing glands (lobules) and more often than not grows in a more diffuse pattern, therefore making detection by a physical exam or mammography more difficult. ILC makes up about 10-15% of invasive cases, and can present in both breasts more often than IDC. 

Non-invasive cancers usually remain confined to their place of origin/growth and do not invade neighboring tissues. Ductal carcinoma in situ (DCIS) is the most common type of non-invasive breast cancer. In DCIS, abnormal cells are confined to the milk ducts and have not penetrated the duct walls. Lobular carcinoma in situ (LCIS) is less common and is more of a marker indicating increased breast cancer risk rather than a true cancerous lesion. In addition, LCIS suggests a higher likelihood of developing invasive cancer in either of the two breasts over time. 

However, beyond anatomical classifications, breast cancers are also characterized by their molecular markers, estrogen receptor (ER) progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). These molecular markers define subtypes with important treatment implications. ER+ and/or PR+ cancers typically respond to endocrine therapies such as tamoxifen or aromatase inhibitors. On the other hand, HER2+ cancers overexpress the HER2 protein and often respond to targeted therapies like trastuzumab. A critical subtype is triple-negative breast cancer (TNBC), which lacks ER, PR, and HER2 expression. For this reason, TNBC tends to be more aggressive, has fewer targeted treatment options, and is more common in younger women. There are also rarer subtypes with distinct behaviors. Tubular, mucinous, and medullary carcinomas generally have more favorable prognoses, while inflammatory breast cancer is an uncommon but aggressive form that presents with redness and swelling of the breast, often without a distinct lump. Paget disease of the nipple is another rarer form associated with underlying DCIS or invasive cancer. 

Works Cited

American Cancer Society. “Types of Breast Cancer.” American Cancer Society, 2024, https://www.cancer.org/cancer/breast-cancer/about/types-of-breast-cancer.html. Accessed 1 Sep. 2025.

National Cancer Institute. “Breast Cancer—Patient Version.” National Cancer Institute, 2024, https://www.cancer.gov/types/breast. Accessed 2 Sep. 2025.

Mayo Clinic Staff. “Breast Cancer — Symptoms and Causes.” Mayo Clinic, 2023, https://www.mayoclinic.org/diseases-conditions/breast-cancer/symptoms-causes/syc-20352470. Accessed 2 Sep. 2025.