Invasive Lobular Carcinoma (ILC)

By NBCF team

Last updated on Mar 25, 2025

Medically reviewed on Oct 30, 2024

by: Lillie D. Shockney

Invasive lobular carcinoma (ILC) key highlights

Invasive lobular carcinoma (ILC) is the second most common form of breast cancer, accounting for approximately 10-15% of invasive breast cancer diagnoses.
ILC is a slow-growing cancer. However, it can be more difficult to detect and diagnose than other types of breast cancer because it tends to grow out in straight lines rather than forming a mass or lump.
ILC is the only type of breast cancer that grows in the lobules (milk glands) of the breast. All other types grow in the milk ducts.
The majority of women diagnosed with ILC are over the age of 55, making it more common in post-menopausal women. However, ILC can occur at any age.

What is invasive lobular carcinoma (ILC)?

Invasive lobular carcinoma (ILC) is invasive breast cancer that begins in the lobules (milk glands) of the breast and spreads into the surrounding breast tissue. ILC can also spread to other parts of the body through the blood and lymphatic systems. “Invasive” refers to the way the cancerous cells spread to, or invade, surrounding breast tissue or other parts of the body.

Invasive lobular carcinoma accounts for 10-15% of breast cancer diagnoses, making it the second most common form of breast cancer. Though mammograms are important for the early detection of breast cancer, they are less likely to detect ILC than other types of breast cancer. Because ILC grows in straight lines rather than in a mass or lump, it doesn’t always appear clearly on a mammogram. Therefore, a breast MRI may be needed to diagnose ILC.

More than 80% of invasive lobular carcinoma is hormone receptor-positive (HR+) breast cancer. In HR+ breast cancer, the cancerous cells have tested positive for estrogen receptors (ER+) and progesterone receptors (PR+) but negative for human epidermal growth factor 2 (HER2-).

Signs & symptoms of invasive lobular carcinoma

Invasive lobular carcinoma typically invades breast tissue by spreading out through the breast, growing in straight lines, rather than forming a tight clump or lump. Though not all breast cancer presents tangible symptoms, the signs and symptoms of invasive lobular carcinoma, if present, may include:

A hard or thickened area in the breast tissue or underarm area (as opposed to a hardened lump)
Any unexplained change in the size or shape of the breast, including swelling or shrinkage (especially if on one side only)
Dimpling anywhere on the breast
Puckering in the skin of the breast
A nipple turned inward (inverted) into the breast
Discharge (fluid) from the nipple (particularly clear or bloody discharge)
A change in the skin texture, discoloration, swelling, or an enlargement of pores in the skin of the breast (some describe this as similar to an orange peel’s texture)
Scaly, red, swollen, or unusually warm skin on the breast, nipple, or areola
Recent asymmetry (unequal or lack of sameness) of the breasts

It is important to remember that not all breast changes are breast cancer. However, all breast changes, including those listed above, should be reported to your doctor promptly.

Causes and risk factors of invasive lobular carcinoma

Like other types of breast cancer, the cause of invasive lobular carcinoma is not clear. While the underlying cause of ILC remains unknown, there are known risk factors for ILC. Risk factors for ILC can be both genetic and lifestyle & environmental.

Genetic risk factors for invasive lobular carcinoma

Genetic risk factors are inherited or passed down from parent to child through the genes. These factors are out of a person’s control and cannot be changed.

Genetic risk factors for invasive lobular carcinoma may include:

Gender: Though men can develop breast cancer, it is nearly 100 times more common in women than in men.
Age: The majority of women diagnosed with ILC are 55 years old or older, though it can happen at any age.
Family and personal medical history: Women with a first-degree relative with breast or ovarian cancer have a higher risk of developing breast cancer. A past personal history of breast cancer also increases a woman’s risk of cancer recurring or coming back.
Menstrual and reproductive history: Beginning your period early (before age 12), late menopause after age 55, having your first child after the age of 30, or never having children at all can increase the risk of developing ILC.
Dense breast tissue: Dense breast tissue makes lumps or other abnormalities harder to detect, increasing the risk of breast cancer. Beginning in September 2024, breast imaging radiologists are required to include how dense the breast tissue is in the mammogram report. Density looks white on a mammogram and breast cancer in the form of ILC is also white, making it hard to differentiate healthy dense breast tissue from ILC cells. If the density of the breast tissue is high, additional imaging, such as an ultrasound or MRI, may be warranted.
Genetic mutations: A mutation (or change) in a breast cancer gene, particularly the CDH1 gene, increases a woman’s risk of developing invasive lobular carcinoma.

Lifestyle & environmental risk factors for invasive lobular carcinoma

Lifestyle & environmental risk factors are avoidable risk factors that are often under a person’s control, meaning they can be managed and reduced.

Lifestyle & environmental risk factors for invasive lobular carcinoma may include:

Lack of physical activity
Poor diet
Being overweight or obese
Drinking alcohol or smoking
Long-term use of certain hormonal replacement therapy (HRT)

How serious is invasive lobular carcinoma?

The severity of invasive lobular carcinoma depends on the stage at diagnosis and how far the cancer has spread. When caught and treated in an early stage, the survival rate for ILC is very good. Survival rates for ILC decline the more progressed the cancer is when first diagnosed.

Because it is difficult to detect through early screening methods, invasive lobular carcinoma can grow large and spread before it is diagnosed, often leading to ILC being diagnosed at a later stage than other breast cancers.

Diagnosing invasive lobular carcinoma (ILC)

Detecting and diagnosing invasive lobular carcinoma can be more difficult than other forms of breast cancer because the cancerous cells of ILC form and grow differently. ILC tends to invade breast tissue by spreading out in straight lines rather than amassing to form a solid clump or lump. Because ILC does not usually form into a solid lump, it is harder to detect through breast self-exams and mammograms. Therefore, other types of diagnostic tests and imaging in addition to a mammogram may be needed to diagnose ILC.

From University Distinguished Service Professor of Breast Cancer at Johns Hopkins School of Medicine, Lillie D. Shockney: “A mammogram, for example, may only show the center of the tumor, making its actual size hard to determine. Picture an octopus with its tentacles being different lengths. The mammogram might see the head of the octopus and none of the tentacles. A breast MRI, however, will show all of the tentacles in most cases. The actual size of the tumor is measured by finding the distance between the longest tentacles. For example, the center of the tumor (octopus head) might only be 2 centimeters but the tentacles measurement from point to point might be 5 centimeters. The size of the tumor, therefore, is declared to be 5 centimeters.”

Diagnostic tests for invasive lobular carcinoma

Mammogram

Though invasive lobular carcinoma is less likely than other breast cancers to be detected through a mammogram alone, it is still a useful diagnostic tool. All women age 40 and over should receive a screening mammogram every year. If an abnormality is detected on a screening mammogram, or if breast cancer symptoms are present, a diagnostic mammogram will likely be performed.

Breast ultrasound

A breast ultrasound uses sound waves to create a detailed image of the breast tissue. Like a mammogram, ILC may be more difficult to detect with a breast ultrasound. However, ultrasound is still a useful diagnostic tool for breast cancer.

Breast MRI

A breast MRI (magnetic resonance imaging) uses magnetic waves and radio energy to provide a detailed image of the inside of the breast. Because of the level of detail an MRI provides, it is the most common and best way that invasive lobular carcinoma is detected and diagnosed.

Breast biopsy

After imaging scans, a breast biopsy will be performed on any suspicious or abnormal areas found in the breast. A biopsy uses a needle to extract tissue or fluid from the suspicious area. It is then studied under a microscope to check for the presence of cancerous cells.

Lab tests

After invasive lobular carcinoma is confirmed through imaging tests and a biopsy, lab tests will be performed to collect more information about the cancer. The results of the lab tests will be compiled into a pathology report, which may include information such as:

Size and stage of the invasive lobular carcinoma
Grade of the invasive lobular carcinoma
Lymph node involvement (whether cancer has spread to the lymph nodes)
Hormone receptor status
HER2 status
Rate of cell growth

Prognostic factors of invasive lobular carcinoma (ILC)

Prognostic factors are the characteristics of specific cancers. After a biopsy, a pathologist will create a pathology report outlining the prognostic factors of the breast cancer, which will be used to determine the best treatment options.

There are 3 specific prognostic factors pathologists look for to help determine ILC treatment:

Estrogen receptor status: The cancer is called estrogen receptor-positive (ER+) if estrogen receptors are found in the cancerous cells. This means that estrogen stimulates these specific ILC cells to grow and multiply. The higher the percentage or ER+ cells, the more favorable this prognostic factor is. When the cells are ER+, hormonal therapy will be recommended as a key part of treatment for prevention of recurrence.
Progesterone receptor status: The progesterone receptor is also determined and, if positive (PR+), is also a favorable prognostic factor.
HER2 receptor status: HER2, or human epidermal growth factor receptor 2, helps determine if the ILC cells are aggressive and overproducing the HER2 protein.

Most invasive lobular carcinoma (ILC) is ER+, PR+, and HER2-. It is also known for being a slower growing breast cancer.

Invasive lobular carcinoma stages

Like other types of breast cancer, invasive lobular carcinoma will be assigned a breast cancer stage between 1 and 4 based on pathology results. Generally, the lower the stage, the less progressed the cancer.

Invasive lobular carcinoma stages are as follows:

ILC Stage	Indication
Stage 1 invasive lobular carcinoma	Stage 1 ILC means that the cancer is small (less than 2 centimeters) and hasn’t spread to the lymph nodes, or may have spread to only a few nearby lymph nodes.
Stage 2 invasive lobular carcinoma	Stage 2 ILC means the cancer is larger (between 2 and 5 centimeters) and may or may not have spread into nearby lymph nodes.
Stage 3 invasive lobular carcinoma	Stage 3 ILC means the cancer is large (more than 5 centimeters) and has spread into nearby lymph nodes or lymph nodes near the collarbone.
Stage 4 invasive lobular carcinoma	Stage 4 ILC means that the cancer has spread to distant areas of the body, commonly the colon, uterus, ovaries, and stomach. This is also called metastatic breast cancer.

Although invasive lobular carcinoma is a slow-growing cancer, it tends to be diagnosed at a later stage because it is harder to detect through mammogram alone. Therefore, breast MRI continues to be the best way to screen for and detect invasive lobular carcinoma.

Stage 4 invasive lobular carcinoma (also called metastatic breast cancer) means that the cancer has spread (metastasized) to distant areas or organs of the body. Unlike other types of invasive breast cancer that commonly spreads to the bones, liver, lungs, and brain, ILC tends to metastasize to the colon, uterus, ovaries, and stomach.

Invasive lobular carcinoma grades

When invasive lobular carcinoma is diagnosed, it will be given a grade. A cancer grade is a numbering system that describes how abnormal the cancerous cells look under a microscope. Cancer grades are not to be confused with cancer stages; they are separate and different.

All breast cancer is graded between 1 and 3. Generally, the lower the grade, the less aggressive the cancer.

Invasive lobular carcinoma grades are as follows:

ILC Grade	Indication
Grade 1	The cancerous cells look much like normal breast cells and tend to grow slowly.
Grade 2	The cancerous cells look much like normal breast cells and tend to grow at a moderate pace (faster than Grade 1).
Grade 3	The cancerous cells look distinctly different from normal breast cells and tend to grow quickly. Grade 3 ILC presents an increased chance of breast cancer recurrence in the future.

Subtypes of invasive lobular carcinoma

There are several subtypes of invasive lobular carcinoma. Subtypes of ILC are assigned based on how the cancerous cells look under a microscope. All subtypes of ILC are usually cared for and treated the same way.

Invasive lobular carcinoma subtypes include:

Classic ILC: The most common subtype, classic ILC refers to small cancer cells that have invaded the stroma, or the connective tissue that surrounds the breast ducts and lobules.
Solid ILC: Solid ILC cells grow in large sheets with little connective tissue (stroma) between them.
Alveolar ILC: A very rare subtype, alveolar ILC is characterized by clusters of ILC cells rather than the usual single-file lines.
Tubulolobular ILC: This type of ILC is a combination of some cells that grow in single-file lines and others that form hollow tube-like structures.
Pleomorphic ILC: A very rare subtype, pleomorphic ILC is characterized by larger cancerous cells with distinctly different centers (nuclei) than other subtypes of ILC.

What is the difference between invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC)?

The main difference between invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC) is where the cancer originates—or begins to form—in the breast. Invasive lobular carcinoma (ILC) forms in the lobules (milk glands) of the breast, while invasive ductal carcinoma (IDC) forms in the milk ducts of the breast.

Invasive lobular carcinoma (ILC) should not be confused with lobular carcinoma in situ (LCIS). LCIS is not breast cancer, despite having “carcinoma” in the name. It is a breast condition in which abnormal, non-cancerous cells are found in the lobules of the breast.

Treatment for invasive lobular carcinoma

Like other types of breast cancer, the regimen chosen to treat invasive lobular carcinoma will vary based on the characteristics of the cancerous cells, the stage and grade of the cancer, the size of the cancerous cells, and the overall health of the patient.

Common treatments for invasive lobular carcinoma include:

Breast cancer surgery

Surgery is often used to treat invasive lobular carcinoma. There are generally two main types of breast cancer surgery for ILC:

Lumpectomy: Also called breast-conserving surgery or partial mastectomy, a lumpectomy removes only the cancerous tumor and a small margin of healthy tissue surrounding it. It is usually used to treat only early-stage ILC when the cancerous cells are small and have not spread. A lumpectomy may be followed by radiation to ensure that all cancerous cells have been destroyed.
Mastectomy: A mastectomy is the surgical removal of the breast and is often used to treat patients with multiple cancerous tumors, later-stage ILC, or a large invasive carcinoma. There are several different types of mastectomies, including total simple mastectomy, skin-sparing mastectomy, modified radical mastectomy, and bilateral (double) mastectomy. A sentinel node biopsy will likely be performed at the time of a mastectomy to determine if the cancer has spread. A mastectomy may be performed with or without breast reconstruction.

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Radiation

Radiation uses high-energy rays to destroy cancer cells and may be used after breast surgery to destroy any ILC left behind and reduce the chance of the cancer coming back. It is often used after a lumpectomy.

Chemotherapy

Chemotherapy uses a combination of oral or intravenous (IV) drugs to destroy cancer cells or slow their growth. The use of chemotherapy depends on the prognostic factors—or features—of the breast cancer, such as hormone receptor and HER2 status. Other factors influencing the decision to use chemotherapy to treat invasive lobular carcinoma include the cancer stage, grade, tumor size, and whether the cancer has spread.

Chemotherapy may be given before surgery (neoadjuvant therapy) to reduce the tumor size, after surgery (adjuvant therapy) to reduce the chance of cancer returning, or both. The patient’s care team will help determine if, when, and what type of chemotherapy to administer to treat ILC. If the ILC is slow growing (Grade 1) then it is likely that chemotherapy may not be of benefit since chemotherapy kills rapidly growing cells. Hormonal therapy may be a better treatment option in that case.

Hormonal therapy

Hormonal therapy uses drugs to block or lower the levels of hormones, such as estrogen and progesterone, in the body, which can help slow or stop the growth of some breast cancers, including invasive lobular carcinoma. It may be given to women with hormone receptor-positive (HR+) invasive lobular carcinoma before or after breast surgery. Hormonal therapy is not used to treat triple-negative breast cancer (TNBC) since TNBC cells lack the necessary hormone receptors.

Targeted therapy

Targeted therapy to treat invasive lobular carcinoma uses drugs that are directed (targeted) at proteins in cancerous cells, most commonly HER2 proteins, slowing down or stopping cell growth. Targeted therapy is directed at specific types of cancerous cells rather than all cells, as in chemotherapy.

Invasive lobular carcinoma prognosis and survival rate

When detected and treated in the early stages, the prognosis for invasive lobular carcinoma is very good. Because ILC is a slow-growing cancer, there is more opportunity to catch it in the early stages when it is easier to treat.

When detected and treated in the early, localized stages, the 5-year relative survival rate of invasive lobular carcinoma is 99%. If ILC is diagnosed at a later stage, has spread into nearby tissue or lymph nodes, or has metastasized to distant areas of the body, the survival rate begins to decline.

Survival rates for invasive lobular carcinoma are grouped into three stages: localized, regional, and distant. Each stage has its own 5-year relative survival rate.

5-year relative survival rates for invasive lobular carcinoma

ILC Stage	5-year relative survival rate
Localized: There is no sign that cancer has spread outside of the breast. Includes only invasive breast cancer, not DCIS.	99%
Regional: The cancer has spread outside of the breast to nearby structures or lymph nodes.	93%
Distant: The cancer has spread to different parts of the body, such as the colon, uterus, ovaries, stomach, or elsewhere.	22%

Table information provided by Cleveland Clinic

Invasive lobular carcinoma recurrence

Invasive lobular carcinoma recurrence is when the cancer is later found to still be present in the body somewhere after initial successful treatment. Recurrence can be local (within the remaining breast tissue) regional (in the lymph nodes under the arm or near the clavicle bone), or a distant, with breast cancer cells appearing in other organs of the body. If ILC returns as a distant recurrence, it commonly reappears in the colon, uterus, ovaries, and stomach.

It’s important to keep in mind that every individual and every cancer is unique. There is no statistic that can accurately predict the chances of a breast cancer recurrence. Hormone receptor-positive (HR+) breast cancers, such as most ILC, tend to have a lower rate of recurrence in the first 5 years after diagnosis than hormone receptor-negative (HR-) breast cancers. However, HR+ breast cancers can recur at a higher rate than HR- cancers 10+ years after treatment.

A recurrence of invasive lobular carcinoma cannot be prevented, but there are ways to lower the risk of recurrence, including:

Staying in contact with your oncologist for follow-up appointments
Taking hormonal therapy exactly as prescribed (if cancer was hormone receptor-positive)
Continuing early detection (mammograms and breast self-exams) on any remaining breast tissue, as recommended by your doctor
Eating well to ensure proper nutrition
Maintaining a healthy weight
Participating in regular physical activity or exercise
Not smoking or drinking alcohol

Sources:
Johns Hopkins Medicine
Mayo Clinic
MD Anderson
National Library of Medicine
breastcancer.org

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