Invasive Lobular Carcinoma on Your Pathology Report

Invasive lobular carcinoma is a type of breast cancer that starts in the lobules. The lobules are the small glands in the breast that make milk. Seeing invasive lobular carcinoma on a pathology report can be confusing, because the words sound alarming and the type gets less attention than ductal cancer. This page breaks the term into its parts and explains what your report is telling you.

Break the name into three pieces.

Carcinoma is a cancer that starts in the cells that line an organ or gland.

Lobular points to where it started. The National Cancer Institute says this cancer begins in the cells that line the breast glands that make milk, called lobules.

Invasive describes behavior, not location in the body. NCI's definition says the cancer has spread beyond where it first formed. That means beyond the lobule into nearby breast tissue. It does not mean the cancer has traveled to other organs. Whether it has spread further is a separate question, answered by staging.

NCI describes invasive ductal carcinoma, which starts in the milk ducts, as the most common breast cancer diagnosis. Lobular cancer is less common, but it is far from rare.

Data from NCI's SEER program show that invasive lobular carcinoma accounts for about 15 percent of new breast cancer diagnoses. That works out to roughly 46,000 lobular diagnoses each year in the United States. It tends to appear at older ages: 67 percent of new lobular diagnoses are in women over age 60.

Both are invasive breast cancers, and both are treated by the same kinds of teams. NCI notes some real differences.

• Starting point. Ductal cancer starts in the cells lining the milk ducts. Lobular cancer starts in the cells lining the lobules.
• Growth. NCI says invasive lobular carcinoma grows more slowly than invasive ductal carcinoma.
• Both breasts. NCI notes lobular cancer is more often found in both breasts than other breast cancer types.
• Receptors. SEER reports 89 percent of new lobular cancers are hormone receptor-positive and HER2-negative, compared with 67 percent of non-lobular cancers.

SEER also notes research showing lobular cancer can come back later than ductal cancer, sometimes more than 10 years after diagnosis. That is one reason long-term follow-up plans matter. It is a topic for your care team, not a reason for alarm.

A report can also mention ductal carcinoma in situ, or DCIS. In situ is the opposite of invasive: the abnormal cells are still inside the ducts. Our page on in situ versus invasive cancer explains that difference.

Many people with a lobular diagnosis ask why imaging did not flag it sooner. Breast density is often part of the answer.

NCI explains that dense breast tissue and some abnormal breast changes both appear as white areas on a mammogram, while fatty tissue appears dark. White on white is hard to read. Because of this, mammography is less sensitive in women with dense breasts, meaning it is more likely to miss cancer. Nearly half of women 40 and older who get mammograms have dense breast tissue, and FDA regulations now require mammography providers to tell women when they do.

For screening, the U.S. Preventive Services Task Force has said there is not yet enough evidence to recommend for or against extra imaging, such as ultrasound or MRI, for women with dense breasts. After a diagnosis, imaging decisions become individual. Ask your team which scans they recommend for you and why, including whether breast MRI would add useful information in your case.

The type is only the first line. Your report will usually also cover:

• Hormone receptor status. Whether the cancer cells carry receptors for hormones such as estrogen. This guides whether hormone-blocking treatment can help.
• HER2 status. Whether the cells carry the HER2 growth protein, which has its own targeted treatments.
• Grade. How abnormal the cells look under the microscope.
• Size and margins, if surgery has already happened.

Take the report with you and have your team go through it with you, line by line. No single word on the page, including "invasive," tells the whole story on its own.

• Breast Cancer Types — National Cancer Institute
• Invasive Lobular Carcinoma — SEER Cancer Stat Facts
• Dense Breasts: Answers to Commonly Asked Questions — National Cancer Institute