Invasive Lobular Carcinoma (ILC)
Invasive lobular carcinoma (ILC) is breast cancer that starts in the lobules, the glands in the breast that produce milk. Invasive means the cancer has spread outside the lobules into surrounding breast tissues.
ILC is different from the more common invasive ductal carcinoma (IDC). IDC starts in the milk ducts, which carry milk from the lobules to the nipple. About 10–15% of breast cancer diagnoses are ILC, compared to around 85%–90% that are IDC.
ILC has a unique biology that makes it behave differently from IDC, making it harder to detect.
Symptoms of invasive lobular carcinoma
In many cases, invasive lobular carcinoma causes no symptoms and is found after your doctor sees a suspicious area on a screening mammogram.
In other cases, you or your doctor may feel a thick or swollen area in your breast. ILC is less likely than other breast cancers to cause a hard lump. This is because lobular breast cancer cells tend to grow in straight lines, forming a sheet rather than a lump.
Any of the following unusual changes in the breast can be a first sign of invasive lobular carcinoma:
swelling of all or part of the breast
skin irritation
skin dimpling, sometimes looking like an orange peel
changes in breast skin texture
breast or nipple pain
nipple discharge, other than breast milk
nipple turning inward (inverted nipple)
redness, scaliness, or thickening of the nipple or breast skin
a lump or swelling in the underarm area
one breast looking bigger than the other
Diagnosis of invasive lobular carcinoma
Invasive lobular carcinoma can be harder to detect than some other types of breast cancer. This is because ILC cells can grow in lines rather than clumps, so there may not be a mass that you can feel or that your doctor can see on a mammogram. Because of this, it’s very important to tell your doctor about any changes in your breasts that could be a symptom of ILC, such as a change in the texture of the skin of the breast or a nipple that turns inward.
Diagnosing invasive lobular carcinoma involves a combination of procedures and almost always includes:
Other imaging tests that may be used to detect invasive lobular breast cancer are:
Listen to The Breastcancer.org Podcast episode featuring Dr. Maxine Jochelson explaining the imaging tests for lobular breast cancer.
Staging invasive lobular carcinoma
The stage of invasive lobular carcinoma is determined by the cancer’s characteristics, such as how large it is and whether or not it has hormone receptors. The stage of the cancer helps you and your doctor:
figure out your prognosis, which is the likely outcome of the disease
decide on the best treatment options for you
determine if certain clinical trials may be a good option for you
Once a diagnosis of invasive lobular carcinoma has been made, your doctor will do more testing to collect information on the characteristics of the cancer. These tests, as well as the results of your biopsy, make up the parts of your pathology report.
Information commonly collected as part of a pathology report include:
Generally, the stage of invasive lobular carcinoma is described as a number on a scale of I through IV.
Stages I, II, and III describe early-stage cancer.
Stage IV, also called metastatic, describes cancer that has spread outside the breast to other parts of the body. Common metastatic sites are the bones and liver. But metastatic ILC also can spread to other sites, such as the stomach and bladder.
Treatment of invasive lobular carcinoma
As with invasive ductal carcinoma, treatments for invasive lobular carcinoma depend on the characteristics and stage of the cancer. Treatments may include surgery, radiation therapy, chemotherapy, hormonal therapy, targeted therapy, and immunotherapy.
Follow-up care after ILC treatment
Because of better diagnostic tests and advances in cancer treatments, people are living longer than ever after being diagnosed with breast cancer. Experts estimate that there are more than 4 million breast cancer survivors in the United States.
Still, because of treatments they’ve received, many breast cancer survivors have a higher risk of developing other diseases as they age, including high blood pressure, heart disease, and osteoporosis. If you’ve completed treatment for invasive ductal carcinoma, it’s important you get good follow-up care.
Your doctor can work with you to create a follow-up care plan that involves regular checkups so they can monitor your overall health, side effects of treatment, and more. Follow-up care plans may include:
the tests you need
which doctors order the tests
a schedule of when you need to have the tests
healthy living recommendations
resources, if you need more information
Subtypes of invasive lobular carcinoma
There are several subtypes of invasive lobular carcinoma, often named for how the cells look under a microscope. The symptoms, diagnosis, staging, treatment options, and survivorship care are the same for all ILC subtypes.
Classic ILC is the most common form of invasive lobular carcinoma and is made up of small cancer cells that invade the stroma, the fibrous connective tissue that surrounds the breast ducts and lobules. Classic ILC cells tend to invade the stroma in a single-file pattern.
Solid ILC cells grow in large sheets with little stroma in between them.
Alveolar ILC cells grow in groups of 20 or more.
Tubulolobular ILC cells grow in a single-file pattern, but some of the cells also form small tube-like structures.
Pleomorphic ILC cells look different from classic ILC cells. The cells are larger and the cells’ nuclei — the core of each cell that contains its genetic material — look different from one another. Pleomorphic ILC also may be composed of signet ring cells, cells that are filled with mucus that pushes the nucleus to one side.
— Last updated on April 29, 2025 at 8:46 PM
