There are dozens of breast cancer types, but they fall into a few major categories that determine how the cancer behaves and how it’s treated. Doctors classify breast cancer in two overlapping ways: by where it starts growing (the tissue type) and by which molecular markers drive its growth (the subtype). Understanding both gives you the full picture.
Invasive vs. Non-Invasive: The First Division
The broadest distinction is whether cancer cells have spread beyond the layer of tissue where they originated. Non-invasive (in situ) breast cancers stay contained within the milk ducts or lobules. Invasive cancers have broken through that boundary and started growing into surrounding breast tissue, which also means they have the potential to spread to other parts of the body.
The two main non-invasive types are ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). DCIS involves abnormal cells inside a milk duct that haven’t spread. It’s often detected on a mammogram before any symptoms appear. LCIS is a bit different: it involves abnormal cells in the milk-producing lobules and is generally considered a risk factor for developing invasive cancer later, rather than an immediate threat on its own.
The Two Most Common Tissue Types
Once breast cancer becomes invasive, it’s named for the tissue where it started. About 8 in 10 invasive breast cancers are invasive ductal carcinoma (IDC), which begins in the cells lining the milk ducts. Another 1 in 10 is invasive lobular carcinoma (ILC), which starts in the lobules. Together, these two account for roughly 90% of all invasive breast cancers.
IDC and ILC can feel different on examination. IDC typically forms a firm, distinct lump. ILC tends to grow in a more diffuse pattern, sometimes thickening the breast tissue rather than forming a noticeable mass. This makes ILC slightly harder to detect on standard mammograms, and it’s more likely to be found in both breasts.
Less Common Tissue Types
Beyond ductal and lobular cancers, several rarer forms each make up fewer than 5% of all breast cancers. These include medullary carcinoma, mucinous (colloid) carcinoma, tubular carcinoma, and papillary carcinoma. Many of these rarer types actually carry a better prognosis than standard IDC, though treatment still depends on the specific characteristics of the tumor.
Inflammatory Breast Cancer
Inflammatory breast cancer (IBC) is an aggressive form that doesn’t usually produce a lump. Instead, cancer cells block lymph vessels in the skin, causing the breast to look swollen, red, and pitted, sometimes resembling an orange peel. It accounts for 1% to 5% of breast cancers and tends to grow quickly, which means it’s often diagnosed at a more advanced stage.
Paget Disease of the Breast
Paget disease involves the skin of the nipple and areola, making up about 1% to 3% of all breast cancers. It often looks like eczema: itching, flaking, crusted or thickened skin, and sometimes a flattened nipple or bloody discharge. Most people with Paget disease also have a tumor deeper in the same breast, though imaging doesn’t always detect it. This type tends to have a slightly less favorable prognosis than other breast cancers.
Phyllodes Tumors
Phyllodes tumors are rare, accounting for about 1% of all breast tumors. They develop in the connective tissue of the breast rather than in the ducts or lobules. They’re graded as benign, borderline, or malignant based on how the tissue looks under a microscope. The majority, roughly 60% to 75%, are benign. Borderline tumors make up 15% to 26%, and malignant phyllodes tumors account for 8% to 20%. Even benign phyllodes tumors are typically removed surgically because they can grow large and may recur.
Four Molecular Subtypes
Tissue type tells you where the cancer started, but molecular subtype tells you what’s fueling it. Doctors test every breast cancer for two key features: hormone receptors (for estrogen and progesterone) and a protein called HER2. The results sort cancers into four molecular subtypes, and this classification often matters more for treatment decisions than tissue type alone.
HR-positive/HER2-negative is the most common subtype. These cancers grow in response to estrogen or progesterone, so treatments that block those hormones are effective. They tend to grow more slowly and generally carry the most favorable prognosis.
HR-positive/HER2-positive cancers respond to both hormones and the HER2 protein. They’re treated with a combination of hormone-blocking therapy and drugs that target HER2. The HER2 component makes them more aggressive than HR-positive/HER2-negative cancers, but targeted HER2 therapies have significantly improved outcomes.
HR-negative/HER2-positive cancers aren’t driven by hormones but overproduce the HER2 protein. These tumors tend to be more aggressive. They have a higher likelihood of spreading to the brain and liver compared to hormone-driven cancers. Targeted HER2 therapies are the cornerstone of treatment.
Triple-negative breast cancer (TNBC) lacks all three markers: no estrogen receptors, no progesterone receptors, and no HER2 overproduction. This means hormone therapies and HER2-targeted drugs don’t work against it, leaving chemotherapy and immunotherapy as the primary options. TNBC accounts for about 10% to 15% of breast cancers, tends to grow faster, and is more common in younger women and Black women.
How Subtype Affects Where Cancer Spreads
When breast cancer becomes metastatic (stage IV), the molecular subtype influences which organs it’s most likely to reach. All subtypes spread to bone most frequently, but the patterns diverge from there.
Hormone receptor-positive cancers have a strong tendency toward bone metastasis and are less likely to spread to the lungs. HER2-positive cancers, regardless of hormone receptor status, are more prone to reaching the liver and brain. Triple-negative breast cancer is relatively more likely to spread to the lungs, though it’s less likely to metastasize to bone than HER2-positive types. These patterns matter because they influence what kind of monitoring doctors recommend for each subtype.
Survival Rates by Stage
The overall five-year survival rate for breast cancer is 91.9%, but that number varies enormously by how early the cancer is caught. For localized breast cancer, meaning it hasn’t spread beyond the breast, the five-year survival rate is effectively 100%. When cancer has spread to nearby lymph nodes (regional stage), that drops to 87.5%. For distant metastatic disease, the five-year survival rate is 33.8%.
These numbers reflect averages across all subtypes. HR-positive/HER2-negative cancers generally have the best outcomes, while triple-negative and HER2-positive cancers historically had lower survival rates, though targeted therapies developed over the past two decades have narrowed that gap considerably for HER2-positive disease.
Breast Cancer in Men
Men can develop breast cancer too, though it’s rare, accounting for less than 1% of all breast cancer cases. The vast majority of male breast cancers are invasive ductal carcinoma. Because men have very little lobular tissue, lobular carcinoma is uncommon. Male breast cancer is strongly associated with mutations in the BRCA1 and BRCA2 genes, and men with a family history of breast cancer on either side should discuss genetic testing with their doctor. The molecular subtypes and treatment approaches are similar to those for women, though most male breast cancers are hormone receptor-positive.