Invasive lobular carcinoma (ILC)

Invasive lobular carcinoma, or ILC, is a type of cancer that grows in the lobules, the milk-producing glands in the breast. The cancer becomes invasive when it moves beyond the lobules into nearby breast tissue.

Invasive lobular carcinoma is less common than invasive ductal carcinoma, which grows in the ducts, or tubes, that carry milk from the lobule to the nipple. Each year, about 10-15% of new breast cancer diagnoses are invasive lobular carcinomas.

Invasive lobular carcinoma cells tend to grow in straight lines, sheets, or a scattered pattern, instead of forming a clump of cells. Invasive lobular carcinoma also can:

• Occur in more than one area of the breast
• Affect both breasts, in about 1 in every 5 cases
• Be mixed with ductal carcinoma cells in a small number of cases

Cases of invasive lobular carcinoma are on the rise. A 2025 report by the American Cancer Society noted that rates of invasive lobular carcinoma increased by nearly 3% per year between 2012 and 2021, versus 0.8% for other breast cancers. More research is needed to figure out why.

Invasive lobular carcinoma is different from lobular carcinoma in situ (LCIS). LCIS isn’t actually breast cancer, but it can raise the risk of developing breast cancer in the future. Lobular carcinoma in situ occurs when there are abnormal changes to cells that line the lobules. These cells remain inside the lobule, or “in situ.”

Who gets invasive lobular carcinoma?

Although men can get invasive lobular carcinoma, it’s much more common in women. ILC can develop at any age, but most cases occur in women who are in their 60s or 70s.

While invasive lobular carcinoma is most common in White women, it affects women of all ethnic backgrounds. The American Cancer Society’s 2025 Lobular breast cancer statistics report showed that rates of diagnosis are increasing more among Asian American and Pacific Islander women than women of other ethnic backgrounds. The reasons for this aren’t yet entirely clear.

Besides simply growing older, many of the risk factors for invasive lobular carcinoma are the same as those for other types of breast cancer. These include:

• Having your first menstrual period at a younger age
• Later age at first birth of a child, or not having children at all
• Later age at menopause
• Gaining excess weight after menopause
• A strong family history of invasive lobular carcinoma or other breast cancer
• Frequent alcohol consumption

Learn more about What causes breast cancer?

Other risk factors for invasive lobular carcinoma

Other risk factors include:

Hormone replacement therapy to treat menopausal symptoms

Some research suggests that hormone replacement therapy can increase the risk of invasive lobular carcinoma. The greatest risk appears to come from long-term use of hormone replacement therapy (5 or more years) in the form of a patch, pill, gel, or cream. When taken this way, the hormones travel throughout the entire body.

Vaginal estrogen, a local treatment, does not appear to increase breast cancer risk. It comes in the form of a cream, ring, or tablet applied directly to the vaginal tissues. A March 2025 study found that low-dose vaginal estrogen could be safely used by women with a history of breast cancer.

Inherited genetic mutations

Inherited genetic mutations are abnormal changes in genes that can be passed through families. Inherited mutations in genes such as BRCA1, BRCA2, TP53, CDH1, and others have been found to increase breast cancer risk.

Research suggests that two of these mutations are more strongly associated with invasive lobular carcinoma:

• BRCA2: BRCA2 mutations are more commonly found in people with invasive lobular breast cancers than BRCA1 mutations are. Mutations in the BRCA1 gene are more common with invasive ductal carcinomas.
• CDH1: Inherited CDH1 mutations aren’t common, but they can increase the risk of invasive lobular carcinoma and other cancers, such as diffuse gastric cancer (a type of stomach cancer). There is often a strong family history of invasive lobular carcinoma and/or stomach cancer.
  • The CDH1 mutation leads to the loss of a protein called E-cadherin. This protein helps neighboring cells stick together and can prevent cells from growing and dividing out of control.
  • If you have an inherited CDH1 mutation, the lifetime risk of breast cancer ranges from 37-55%. Most of these are lobular breast cancers.

Other inherited mutations that can increase risk for invasive lobular carcinoma include ATM, CHEK2, and PALB2.

Learn more about Genetic testing for inherited mutations.

A past diagnosis of lobular carcinoma in situ (LCIS)

Lobular carcinoma in situ (LCIS) is a condition in which abnormal cells are found inside the breast lobules. It is important to know that LCIS is not cancer.

People with LCIS don’t always develop breast cancer. However, they are considered to have a higher risk of breast cancer — including DCIS, invasive lobular carcinoma, and invasive ductal carcinoma — than the general population.

A past diagnosis of atypical lobular or ductal hyperplasia

Two conditions involving abnormal cell growth, atypical lobular hyperplasia and atypical ductal hyperplasia, can increase the risk of invasive lobular or ductal carcinoma in either breast.

Atypical lobular hyperplasia is abnormal cell growth inside breast lobules.

Atypical ductal hyperplasia is abnormal patterns of cell growth inside breast ducts.

If either of these conditions is found on a biopsy, doctors may recommend:

• Removing more areas of tissue around it to confirm there are no cancerous cells nearby
• Regular follow-up breast exams and imaging

Symptoms of invasive lobular carcinoma

Invasive lobular carcinoma cells tend to grow in single-file lines, sheets, or dispersed patterns, instead of forming a lump like other types of breast cancer. The cancer cells don’t have the protein known as E-cadherin, which helps cells stick together.

Because of this growth pattern, invasive lobular carcinoma can be harder to detect using manual breast exams and screening mammograms. Invasive lobular carcinoma can grow slowly for many years until it’s found.

While invasive lobular carcinoma may form a noticeable lump as it grows larger, it can cause other breast changes first. These may include:

• Nipple turning inward (inversion) or becoming flatter (retracted)
• Changes to the breast skin, such as thickening, puckering, or dimpling
• Breast fullness or swelling
• A feeling of tightness or pulling in the breast
• Nipple discharge

It’s important to pay attention to any breast changes and report them to your doctor. Keep up with clinical breast exams and recommended breast cancer screenings, too.

How invasive lobular carcinoma is diagnosed

A combination of the following tests is often used to diagnose invasive lobular carcinoma:

• Breast exam by your healthcare provider
• Mammogram: An imaging test that takes X-rays of the breast from different angles. If you have risk factors for invasive lobular carcinoma, your healthcare team may recommend contrast-enhanced digital mammography. It uses an intravenous contrast dye to make it easier to see any cancer. (This technology isn’t available everywhere.)
• Breast ultrasound: A test that uses soundwaves to create images of the breast tissue.
• Breast MRI: Uses magnetic fields and radio waves to create pictures of the breast tissue. It can be a better option than mammography for finding invasive lobular carcinoma.
• Biopsy: A biopsy is a procedure that removes a sample of the abnormal tissue. Doctors can perform a biopsy using a needle device or with minor surgery to remove some or all of the suspicious area.

After a biopsy to remove a tissue sample, a pathologist, a doctor who specializes in diagnosing diseases, examines the tissue under a microscope and tests it for certain features. In some cases, the pathologist may decide to have the cells tested for the protein E-cadherin to confirm the diagnosis. Loss of this protein is often a key feature of invasive lobular carcinoma cells.

After the pathologist completes tissue examination and testing, you and your doctor will receive a pathology report that includes the cancer’s cell type, grade (how different the cancer cells look from normal cells), hormone receptor status, HER2 status, and other features of the invasive lobular carcinoma.

Subtypes of invasive lobular carcinoma based on cell appearance

Invasive lobular carcinoma is often described based on the appearance of the cancer cells. Subtypes include:

• Classic: Small cancer cells invade the stroma, the connective tissue surrounding the breast ducts and lobules, in a single-file pattern. This is the most common type.
• Solid: The cells grow in large sheets.
• Alveolar: The cells grow in larger groups.
• Tubulolobular: Some cells grow in a single-file pattern, while others form small tube-like structures.
• Pleomorphic: The cells tend to be larger, and the nuclei, or cell centers, look very different from each other. There also may be cells filled with mucus that pushes the nucleus to one side. This is a rare subtype that is often more aggressive than other subtypes.

All subtypes are treated in basically the same way. Because pleomorphic invasive lobular carcinoma tends to be more aggressive, it may require more intensive treatment.

Subtypes of invasive lobular carcinoma based on other test results

Other features of the cancer can be helpful in developing the treatment plan. For example:

If tests show that cancer cells have proteins called hormone receptors, it is hormone receptor-positive. This means the hormones estrogen and/or progesterone are helping the cancer grow. Most invasive lobular carcinomas are hormone receptor-positive. Your care team will recommend hormonal therapy and possibly other treatments, such as targeted therapy.

If the cancer cells have too many copies of a gene called HER2, testing will confirm the presence of HER2 receptors. The cancer may be called HER2-positive, HER2-low, or HER2-ultralow. This has to do with what testing reveals about what levels of HER2 are present. Treatment would include anti-HER2 targeted therapy. Most invasive lobular carcinomas are HER-negative, so they’re generally not treated with anti-HER2 therapy.

If the cancer does not have hormone receptors or HER2 receptors, it called triple-negative. Treatment may include targeted therapy and/or immunotherapy. However, only about 1 to 3% of invasive lobular carcinomas are triple-negative, making this a rare subtype.

While some features of the cancer are listed on the pathology report after your biopsy, the stage is confirmed after surgery to remove the breast cancer and confirm whether or not cancer is in the lymph nodes. Learn more about How breast cancer is staged.

You also might hear your doctor describe the cancer using categories such as luminal A, luminal B, basal-like, or HER2-enriched. These are more detailed classifications that include hormone and HER2 receptor status, grade, rate of growth, and other factors. Most invasive lobular carcinomas are luminal A type. These cancers are hormone receptor-positive, HER2-negative, and slower-growing. Visit Molecular subtypes of breast cancer to learn more.

Additional testing after a diagnosis of invasive lobular carcinoma

After being diagnosed with invasive ductal carcinoma, your doctor may suggest some additional tests to help guide your care.

Testing for inherited genetic mutations

Sometimes, changes in our genes — called genetic mutations — can increase the chance of developing cancer. These changes can also run in families. The American Society of Clinical Oncology recommends that anyone newly diagnosed with breast cancer before age 65 be tested for changes in the BRCA1 and BRCA2 genes. Testing may also be helpful for:

• People over 65, depending on their personal and family history
• People who might benefit from certain targeted treatments called PARP inhibitors
• Anyone who has developed a second breast cancer, either in the same breast or the other one

Genetic test results can help you and your care team choose the best treatment options and understand your chances of breast cancer returning in the future. They can also give your family important information about their own possible risks.

Your doctor might also suggest testing for mutations in other genes — such as CDH1, PALB2, ATM, CHEK2, TP53, PTEN, and STK11 — depending on your medical and family history. Your healthcare team can explain how these results might guide your treatment and help family members learn more about their own risk. You can read more about this in Genetic testing for inherited mutations.

Genomic testing for early-stage breast cancer

Genomic tests may be recommended after an early-stage invasive lobular carcinoma diagnosis. These tests:

• Look at the activity of groups of genes to estimate the chance of the cancer coming back.
• Help predict whether treatments such as chemotherapy or hormone therapy are needed to reduce the risk of recurrence. Examples include MammaPrint, Oncotype DX Recurrence Score, and Prosigna.

Researchers are working to develop new genomic tests that may be better at predicting how invasive lobular carcinoma is likely to behave. One example is a test called LobSig.

Next-generation sequence tests for metastatic breast cancer

For metastatic breast cancer, your doctor may recommend a type of genomic test called next-generation sequencing. This test looks at many genes at once to find changes that can be matched with a treatment.

Metastatic invasive lobular carcinoma

If invasive lobular carcinoma moves beyond the breast to other parts of the body, it’s called metastatic invasive lobular carcinoma. Another term for this is stage IV breast cancer.

In some cases, the cancer is stage IV at the time of diagnosis. In others, metastatic invasive lobular carcinoma can develop a decade or more after diagnosis and treatment.

Like other forms of breast cancer, invasive lobular carcinoma can move into organs such as the:

• Brain
• Bones
• Liver
• Lungs

Because invasive lobular carcinoma cells don’t clump together, they also can move along the linings of organs in other areas of the body. These include:

• Gastrointestinal (GI) organs, such as the stomach or intestines
• Urinary tract (kidneys, bladder, urethra)
• Female reproductive organs, such as the ovaries or uterus
• Brain and spinal cord
• Abdominal cavity (the peritoneum)
• Tissues around the eye

Your doctor can use a combination of tests to diagnose metastatic invasive lobular carcinoma. These include:

• Imaging tests: X-rays, CT or PET scans, bone scans, and MRI
• Blood tests
• Physical exams
• Surgical biopsies

If you’re diagnosed with metastatic invasive lobular carcinoma, ask your healthcare team about biomarker testing, including next-generation sequencing tests that may be able to help match the cancer with a specific treatment.

Visit Tests for metastatic breast cancer to learn more.

Treatment for invasive lobular carcinoma

Like any form of breast cancer, invasive lobular carcinoma is treated based on its stage, grade, and the features of the cancer cells.

Compared to ductal carcinoma, invasive lobular carcinoma is more likely to:

• Be hormone receptor-positive and HER2-negative. This means that hormonal therapy is likely to be recommended, but HER2-targeted therapies aren’t. Also, the immunotherapies used to treat triple-negative breast cancer would rarely be used. Triple-negative cancers test negative for estrogen and progesterone receptors as well as HER2 receptors.
• Be diagnosed in both breasts rather than one. It also may be found in multiple areas within the same breast. In these cases, mastectomy may be recommended over lumpectomy (breast-conserving surgery).
• Grow more slowly. This means it may not be as responsive to chemotherapy, which targets fast-growing cells. However, research has shown the chemotherapy is effective for invasive lobular carcinoma that has a high risk of recurrence.

Treatment options for invasive lobular carcinoma

Your treatment plan may include:

• Surgery, including lumpectomy or mastectomy and lymph node removal to check for cancer in the lymph nodes
• Chemotherapy
• Targeted therapy
• Radiation therapy
• Hormonal therapy

Immunotherapy is not usually recommended because it’s only used to treat triple-negative breast cancer. Only about 1 to 3% of invasive lobular carcinomas test negative for estrogen and progesterone receptors and HER2 receptors.

Surgery and radiation therapy are not usually recommended for metastatic breast cancer. They may be used in certain cases if they can help improve symptoms. Learn more about treatment for metastatic breast cancer.

Protecting fertility if you are premenopausal

If you haven’t gone through menopause and you want to have biological children, it’s a good idea to discuss fertility preservation with your doctor before beginning treatment.

Certain breast cancer treatments, including chemotherapy and hormonal therapy, can affect your ability to conceive or may impact the timing of a future pregnancy. Even so, there are ways to plan for having a child. You can request a referral to a fertility specialist, who can walk you through the options available to you.

Follow-up care for invasive lobular carcinoma

You and your care team will decide on a follow-up plan that makes sense for you. Close follow-up is important, given that invasive lobular carcinoma appears to have a higher risk of recurring later on (5 to 10 years after finishing treatment) than other types of breast cancer. People with invasive lobular carcinoma also may be at higher risk of developing another cancer in the opposite breast.

Your doctor likely will follow you more closely if the cancer has a high risk of recurrence, based on features and test results, or is metastatic.

Your care plan may include:

• Physical exams every few months
• Breast imaging with mammography, ultrasound, and/or MRI
• Other imaging tests, as needed, to check on any areas of metastatic breast cancer
• Tests to monitor for treatment side effects, such as impact on heart health or bone health

Visit When to have follow-up visits to learn more.