Invasive Lobular Carcinoma

April 10, 2025

This page was reviewed under our medical and editorial policy by Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Invasive lobular carcinoma (ILC) is the second most common type of breast cancer, after invasive ductal carcinoma. About 10% of people diagnosed with breast cancer have ILC.

Sometimes ILC is referred to as infiltrating lobular carcinoma. It is called infiltrating or invasive because the cancer has spread into surrounding breast tissue and sometimes to other places in the body. Lobular refers to the breast lobules where the cancer begins, and carcinoma means cancer that forms in the tissues or skin that line organs and body structures.

What Is Invasive Lobular Carcinoma?

Invasive lobular carcinoma begins in the lobular (glandular) tissues lining the milk-producing breast glands (lobules). The breast lobules are tiny sacs that almost resemble a strand of grapes deep inside the breast. ILC sometimes forms from lobular carcinoma in situ (LCIS), a noncancerous condition marked by abnormal cells in this area.

ILC spreads out from the lobule tissues to surrounding breast tissue and may also grow in local lymph nodes and distant parts of the body.

Invasive lobular breast cancer is more likely to impact both breasts (bilateral cancer) than other types of invasive breast cancer. It is bilateral for about 20% of women diagnosed with the disease.

Since men have little lobular (glandular) tissue, ILC is uncommon in males and accounts for just 2% of male breast cancer diagnoses.

Is It an Aggressive Cancer?

ILC breast cancer may be either slow-growing, aggressive or somewhere in between, depending on its grade. The grade is how abnormal the cancer cells look and how they grow and form as compared to normal breast cells. It is important for doctors and patients to understand the cancer’s grade because this may affect the treatment options recommended.

ILC is given a grade by a doctor known as a pathologist, who studies cells and tissues under a microscope to diagnose diseases. If the pathologist gives ILC cancer a Grade 3, it is considered aggressive, meaning it will likely be fast-growing.

However, most ILC is hormone receptor-positive (HR+), which means the cancer cells have estrogen or progesterone receptors (or both) on them. HR+ breast cancer tends to grow more slowly than hormone receptor-negative (HR-) cancer cells. The two types of cancer are also treated differently, which is why it is important for the doctor to check the ILC hormone status before creating a treatment plan.

What Causes Invasive Lobular Carcinoma?

The exact cause of ILC is not yet known.

Many personal, lifestyle and genetic factors may increase a person’s risk for developing ILC. However, having one or more of these risk factors does not mean ILC will form. Researchers continue to look into how and why the cancer develops.

Gene mutations may play a role in triggering ILC. Gene changes (mutations), such as on the CDH1 gene for the protein e-cadherin, which is responsible for guiding the production of a protein that helps cells properly stick together and suppress tumor growth, have been linked to ILC. Other possible gene links to ILC, or the transition of lobular carcinoma in situ to ILC, include changes in:

• TP53
• PIK3CA
• FOXA1
• ZNF703
• FGFR1
• BCAR4

Medical and family risk factors for the disease may include:

• Having lobular carcinoma in situ
• A family history of ILC

Risk factors that increase hormone exposure (estrogen and progesterone) over time, which may fuel ILC, include:

• Use of postmenopausal hormone replacement therapy
• Being postmenopausal and overweight because fat tissue in this group of women may raise estrogen levels
• Starting menstruation early (especially before age 12)
• Being older when first getting pregnant (giving birth after age 30)
• Never giving birth
• Going through menopause later (after age 55)
• Using alcohol

Invasive Lobular Carcinoma Symptoms

ILC typically forms in a single-file linear (line) pattern and does not always show symptoms, especially in its early stages. It tends to grow outward, and the cells do not always form a solid tumor. Detection of the disease tends to happen when the cancer is at an advanced stage.

If symptoms are present, they may include:

• Nipple thickening
• A lump in the breast tissue
• A scab on the breast skin that leaks fluid
• Red, flushed or swollen breast skin (breast cancer rash)

When the breast cancer has spread (metastasized) to distant parts of the body, some people may experience:

• Lymph node swelling
• Bone pain
• Shortness of breath
• Weight loss

Diagnosing Invasive Lobular Carcinoma

Because ILC breast cancer typically forms in single-file lines and has a tendency to occur in more than one place (multifocal), including in both breasts (bilateral), it may be more difficult to diagnose than other types of breast cancer.

Magnetic resonance imaging (breast MRI) scans: These scans use magnets, radio waves and a computer to produce detailed breast images, and are beneficial in discovering the size, shape and locations of ILC tumors. For hormone receptor-positive multifocal ILC in older women who are at high risk of the disease, MRI has been shown to be an appropriate diagnostic tool compared to mammograms.

Breast ultrasound scans: These scans use sound waves to take pictures of breast tissue and may help improve the sensitivity of mammogram scans in detecting ILC when the two tests are used together for annual breast cancer screenings.

Breast biopsy to diagnose ILC: Diagnosing ILC also includes doctors taking a tissue sample (breast biopsy) from the patient’s breast to be analyzed and tested in the laboratory by a pathologist. For ILC, one key protein that is often lacking in cancer tissues is e-cadherin, and the absence of this protein is one key indicator that ILC may be present.

Invasive Lobular Carcinoma Stages

People diagnosed with ILC are given a stage of the disease, which is the amount of cancer in the body.

Higher-numbered stages are sometimes referred to as advanced cancer, while lower-numbered stages are sometimes called early-stage cancers.

There are four main stages of ILC, with Stage 3 further divided into substages.

Stage 1: A small breast tumor is found that may or may not have spread to area lymph nodes.

Stage 2: Either a tumor that is about three-quarters of an inch to about 2 inches in size is found along with small amounts of cancer in a few lymph nodes, or a tumor larger than 2 inches is found with no cancer in the lymph nodes. The third possibility for this stage is that no tumor is found in the breast, but cancer is found in axillary (armpit) or breastbone-area lymph nodes.

Stage 3a: Either a tumor larger than 2 inches is found, along with cancer in at least three axillary or breastbone-area lymph nodes, or the cancer has spread into five to nine nearby lymph nodes but not beyond.

Stage 3b: The tumor has spread into the chest wall (fat, muscles, bones and tissues) or breast skin, and sometimes into the axillary lymph nodes, but not to other parts of the body.

Stage 3c: The cancer has spread to at least 10 axillary lymph nodes and sometimes into the breast wall or skin, but not to distant body parts.

Stage 4: The cancer has spread to distant sites in the body, such as the bones, lungs or brain.

The care team assesses many tumor and microscopic cell features to determine breast cancer stage, including:

• How fast cancer cells are growing
• Tumor size
• How many lymph nodes have cancer cells
• If the cancer has spread (metastasized) beyond the breast
• If a protein called HER2 is present in high amounts (HER2 status)
• If the cancer is HR+ (estrogen or progesterone receptor-positive)
• Cancer grade

Sometimes the odds of the cancer coming back (recurring) is also part of staging breast cancer.

Invasive Lobular Carcinoma Grades

In addition to receiving a cancer stage, patients diagnosed with ILC receive a cancer grade. The grade is the degree to which cancer cells are similar to normal cells, and it is one factor pathologists use to help determine the cancer’s stage.

The Nottingham system helps the care team determine a Grade of 1 to 3 by measuring the following features in the cancer cells:

• The cancer cells’ reproduction rate (mitosis), which is usually low for ILC
• Variations in cell size and shape (pleomorphism)
• Tubular (tubule-like) formation

Each of these features is measured and their scores are combined to assign a final Grade of 1, 2 or 3.

Grade 1

Well-differentiated or Grade 1 invasive lobular carcinoma has cells that are usually arranged in a cord-like formation. This is typically a slow-growing cancer with a good chance of recovery (prognosis). It scores 3 to 5 overall on its key cell features.

Grade 2

Most ILC tumors are Grade 2. Invasive lobular carcinoma Grade 2 is also called moderately differentiated. The cells look more abnormal than Grade 1 cancer cells, and the cancer tends to grow and spread somewhat faster. Its score is 6 to 7 on its cell features overall.

Grade 3

Not many ILC tumors are Grade 3 or poorly differentiated. These are cancer cells that typically grow and spread quickly, and the prognosis is worse than it is for Grade 1 and Grade 2 ILC cancer. It scores 8 to 9 on its cell features.

Invasive Lobular Carcinoma Treatment

Patients typically receive more than one type of treatment for ILC breast cancer, and the therapies and procedures recommended by the care team depend on:

• The cancer’s stage and grade
• If the cancer is HR+
• If the cancer tumors are multifocal (there is more than one tumor)
• If the cancer tumors are found in both breasts (bilateral)
• If certain biomarkers (such as certain genes or proteins) are present on the cancer cells
• The patient’s overall health, personal goals and treatment preferences

These treatments are commonly used for ILC.

Breast cancer surgery: Surgery to remove the breast cancer tumors, margins (tissue surrounding the area known to have cancer) and sometimes lymph nodes is done in the majority of ILC cases. If the tumors are not multifocal or in both breasts, breast-conserving surgery (BCS) to remove part of the breast may be performed. Mastectomy to remove each whole breast may be recommended for multifocal and bilateral ILC tumors.

Radiation therapy for breast cancer: A machine and high-energy particles such as X-rays are used to destroy the cancer cells. It may be given after breast-conserving surgery and sometimes after mastectomy. Radiation therapy may also be given to patients with advanced-stage metastatic breast cancer to help manage their symptoms and improve their quality of life.

Depending on the cancer’s stage, hormone status and biomarker status, certain drug treatments may also be given for ILC before, after or sometimes instead of surgery.

Hormone therapy for HR+ ILC: This treatment uses drugs that reduce estrogen or progesterone levels in the body or help block estrogen and progesterone receptors so that the cancer cells cannot feed off of these hormones and grow.

Chemotherapy for breast cancer: This therapy uses cancer-fighting drugs to destroy cancer cells, although this form of treatment has shown low successfulness for ILC.

Targeted drug therapy for breast cancer: This treatment focuses on blocking certain proteins that sometimes help ILC cancer cells thrive.

Invasive Lobular Carcinoma Survival Rate

Survival rates for breast cancer often include ILC along with invasive ductal carcinoma (IDC) and other breast cancer types for an overall rate. For example, the five-year relative survival rate for women who received treatment for any type of breast cancer during its early stages was almost 100% (99.6%) between 2014 and 2020. For regional breast cancer that spread to nearby lymph nodes, this rate was 86.7%, and for distant breast cancer that spread outside the breast to other areas of the body, it was 31.9%.

ILC tends to be diagnosed in more advanced stages compared to IDC, and also is more likely to recur later, making it sometimes more challenging to treat.

In a 2022 study in the Journal of the National Cancer Institute, researchers looked at the survival rates of over 32,000 U.S. patients with breast cancer to look at the differences between ILC and IDC. They found that:

• The estimated 10-year overall survival rate for patients with ILC is 69.6%
• The estimated 10-year overall survival rate for patients with ER+ ILC is 72%

ILC in men is very rare. According to the American Cancer Society, for men, the five-year relative survival rate for ILC, IDC and other types of breast cancer combined is:

• 95% when it’s still in the breast tissue
• 84% when it has spread to area lymph nodes
• 20% when it has spread to distant parts of the body

ILC Care at City of Hope

At City of Hope, advanced testing options are available to elevate the ILC diagnostic process, with the aim of diagnosing the disease as early as possible. Treatment plans are then created and administered by a comprehensive care team with years of breast cancer therapy experience and a passion for patient advocacy, support and prioritizing the individual’s needs and goals during their treatment journey.