Invasive ductal carcinoma is the most common type of breast cancer, representing over 80% of all breast cancer diagnoses in the United States each year. Sometimes called “breast cancer of no special type,” it starts in the milk ducts and breaks through into surrounding breast tissue. With an estimated 321,910 new cases of female breast cancer projected for 2026, this single type accounts for the vast majority.
Where Invasive Ductal Carcinoma Starts
Your breasts contain a network of ducts, which are small tubes that carry milk from the milk-producing glands (lobules) to the nipple. Invasive ductal carcinoma begins when abnormal cells in the lining of these ducts start growing out of control and eventually push through the duct wall into the surrounding breast tissue. Once the cancer breaks beyond the duct, it can reach nearby lymph nodes or enter the bloodstream, potentially spreading to other parts of the body.
This is what separates invasive ductal carcinoma from its non-invasive counterpart, ductal carcinoma in situ (DCIS). DCIS involves the same abnormal cell growth inside the milk ducts, but the cells haven’t broken through the duct wall. DCIS accounts for about 20% to 25% of new breast cancer cases each year and is classified as stage 0. Not all DCIS progresses to invasive cancer, but it’s typically treated to reduce that risk.
How It Compares to Other Types
The second most common type is invasive lobular carcinoma, which starts in the lobules rather than the ducts. It makes up 10% to 15% of breast cancer diagnoses. Lobular cancers tend to grow differently, spreading in a single-file pattern through tissue rather than forming a distinct lump, which can make them harder to detect on standard mammograms.
Beyond these two, there are several less common subtypes (inflammatory breast cancer, Paget’s disease of the nipple, and others), but they collectively represent a small fraction of cases. When people talk about breast cancer in general terms, they’re usually talking about invasive ductal carcinoma.
Molecular Subtypes and Why They Matter
The physical type of breast cancer (ductal vs. lobular) is only part of the picture. Doctors also classify tumors by their molecular profile, which looks at whether the cancer cells have certain receptors on their surface. These receptors determine how the cancer grows and which treatments will work against it.
The three key markers are hormone receptors for estrogen and progesterone (called HR-positive when present) and a protein called HER2 that promotes cell growth. The most common molecular subtype by far is HR-positive, HER2-negative. It accounts for about 70% of all female breast cancers. These tumors grow in response to hormones, which means therapies that block estrogen can be highly effective against them.
Triple-negative breast cancer, which lacks all three receptors, makes up a smaller share and is generally more aggressive because it doesn’t respond to hormone-blocking treatments. HER2-positive cancers, while historically harder to treat, now have targeted therapies that have dramatically improved outcomes.
How It’s Found
Invasive ductal carcinoma is often detected through routine screening mammography before any symptoms appear. On imaging, these tumors typically show up as an irregular mass, sometimes with tiny calcium deposits (calcifications) that form distinct patterns. Ultrasound is frequently used alongside mammography, where the tumor often appears as a shadowy mass with irregular or spiky edges.
When a suspicious area is found, a biopsy removes a small sample of tissue. A pathologist examines the cells under a microscope and assigns a grade from 1 to 3: well-differentiated (grade 1) means the cancer cells still look somewhat like normal cells and tend to grow slowly, while poorly-differentiated (grade 3) means the cells look very abnormal and are more likely to grow quickly. The biopsy also tests for the hormone receptors and HER2 status that guide treatment decisions.
Treatment Overview
Surgery is the primary treatment. The two main options are a lumpectomy, which removes the tumor while preserving the rest of the breast, and a mastectomy, which removes all the breast tissue. During either surgery, doctors typically check the sentinel lymph nodes (the first nodes where cancer would spread) to see whether cancer cells have traveled beyond the breast. If cancer is found in those nodes, additional lymph nodes may be removed.
Most people receive some combination of additional therapies based on their tumor’s molecular subtype. For the majority of cases that are HR-positive and HER2-negative, treatment usually includes endocrine therapy, which blocks the body’s hormones from fueling cancer growth. This is often taken as a daily pill for five to ten years after surgery. Premenopausal patients may also need treatment to suppress ovarian function.
HER2-positive cancers are treated with targeted therapies designed to block the HER2 protein, often combined with chemotherapy. Triple-negative breast cancers, which lack targetable receptors, rely primarily on chemotherapy, sometimes paired with immunotherapy. In many cases, systemic therapy is given before surgery (called neoadjuvant therapy) to shrink the tumor, or after surgery (adjuvant therapy) to reduce the chance of recurrence.
Survival Rates by Stage
Outcomes for breast cancer depend heavily on how early it’s caught. When the cancer is still localized, meaning it hasn’t spread beyond the breast, the five-year relative survival rate is 100%. That figure reflects the fact that people with localized breast cancer are just as likely to be alive five years later as people without the disease.
When the cancer has spread to nearby lymph nodes (regional stage), the five-year relative survival rate is about 87.5%. About 27% of breast cancers are diagnosed at this regional stage. Cancers caught before they reach the lymph nodes have the best prognosis, which is a major reason routine mammography screening is so valuable. Most invasive ductal carcinomas found through screening are detected at earlier, more treatable stages.