The two main types of breast cancer are ductal carcinoma and lobular carcinoma, named for where they start growing in the breast. Ductal carcinoma begins in the milk ducts, while lobular carcinoma begins in the milk-producing glands (lobules). Together, these two types account for roughly 9 out of 10 breast cancer diagnoses. Each type can also be classified as either non-invasive or invasive, which describes whether the cancer has spread beyond where it started.
Ductal Carcinoma: The Most Common Type
About 8 in 10 invasive breast cancers are ductal carcinomas. This type starts in the cells that line a milk duct, then breaks through the duct wall and grows into surrounding breast tissue. Ductal carcinoma often forms a distinct lump that can be felt during a physical exam or spotted on a mammogram, which makes it somewhat easier to catch early compared to lobular carcinoma.
Ductal carcinoma also has a non-invasive form called ductal carcinoma in situ (DCIS). In DCIS, abnormal cells are contained inside the milk duct and haven’t spread into nearby tissue. DCIS is considered a pre-cancer. It’s typically treated with surgery to remove the affected area, sometimes followed by radiation therapy, and possibly hormone therapy depending on the characteristics of the cells.
Lobular Carcinoma: Harder to Detect
About 1 in 10 invasive breast cancers are lobular carcinomas. Instead of forming a firm lump like ductal carcinoma tends to, lobular carcinoma often grows in a single-file pattern through breast tissue. This makes it harder to detect on both physical exams and mammograms.
Lobular carcinoma is also more likely to affect both breasts. About 1 in 5 women with invasive lobular carcinoma have cancer in both breasts at the time of diagnosis. Because it’s harder to spot on standard imaging, lobular carcinoma may require additional imaging methods like MRI for accurate detection.
Non-Invasive vs. Invasive: A Critical Distinction
Beyond where cancer starts, the other major way to classify breast cancer is by whether it has spread. Non-invasive (in situ) breast cancer stays contained in its original location. Invasive breast cancer has broken through the walls of the duct or lobule and spread into surrounding breast tissue, which also means it has the potential to reach lymph nodes and other parts of the body.
This distinction has a significant impact on outlook. When invasive breast cancer is caught while still localized to the breast, the five-year relative survival rate is over 99%. If it has spread to nearby lymph nodes (regional stage), that rate drops to 87%. If it has spread to distant organs, the five-year survival rate is 33%. The overall five-year survival rate across all stages is 92%.
Molecular Subtypes and Receptor Status
Once breast cancer is diagnosed, doctors also classify it by what’s driving the cancer cells to grow. This is based on whether the cancer cells have certain receptors on their surface, and it directly shapes treatment decisions. There are four main molecular subtypes:
- Luminal A: The cancer cells have estrogen and progesterone receptors and tend to grow slowly. This is the most common subtype and generally has the best prognosis.
- Luminal B: Also hormone receptor-positive, but these cancers grow faster than Luminal A. They may or may not have HER2 receptors (a protein that promotes cell growth).
- HER2-enriched: These cancers lack hormone receptors but have high levels of the HER2 protein. They grow quickly but can be treated with therapies that specifically target HER2.
- Triple-negative: These cancers lack estrogen receptors, progesterone receptors, and HER2. This is the most aggressive subtype and has fewer targeted treatment options, so chemotherapy plays a larger role.
Both ductal and lobular carcinomas can fall into any of these molecular subtypes. Two people with ductal carcinoma might receive very different treatments depending on their receptor status.
Less Common Types
A small number of breast cancers don’t fit neatly into the ductal or lobular categories.
Inflammatory breast cancer accounts for 1 to 5% of cases. It’s aggressive and looks different from typical breast cancer. Instead of a lump, the main warning signs are swelling, redness, and warmth in the breast. The skin may look dimpled or puckered, and the nipple may pull inward. These changes tend to develop quickly, within weeks or months. Inflammatory breast cancer is hard to detect on a mammogram because it often doesn’t form a distinct mass.
Paget disease of the breast is a rare form that affects the skin of the nipple or the darker area surrounding it. Symptoms include itching, burning, redness, or flaking of the nipple skin, along with possible bloody or yellowish discharge. It’s found in about 1 to 4% of breast cancers and is usually diagnosed alongside either DCIS or an invasive cancer elsewhere in the breast.
How Treatment Differs by Type and Stage
For non-invasive DCIS, treatment typically involves surgery (either removing the affected area or, less commonly, the entire breast), potentially followed by radiation and hormone therapy. Because DCIS hasn’t spread, the goal is to prevent it from becoming invasive.
For invasive breast cancer at stages I through III, treatment usually starts with surgery. If the tumor is small enough, a lumpectomy (removing just the tumor and a margin of surrounding tissue) is often the first step. For larger tumors or cancer in multiple areas, a mastectomy may be recommended. Surgeons typically also check the nearest lymph nodes during the procedure to see if the cancer has spread.
After surgery, additional treatment depends on the cancer’s molecular profile. Hormone receptor-positive cancers are treated with hormone therapy that blocks estrogen or progesterone from fueling growth. HER2-positive cancers receive targeted therapies designed to interfere with that specific protein. Triple-negative cancers, which lack these treatment targets, rely more heavily on chemotherapy. Radiation therapy after surgery is common for most types and reduces the chance of cancer returning in the same area.
For larger tumors, chemotherapy or targeted therapy may be given before surgery to shrink the tumor and make it easier to remove. This approach, called neoadjuvant therapy, also gives doctors early information about how well the cancer responds to treatment.