Invasive Lobular Carcinoma

Medically Reviewed by Elmer Huerta, MD, MPH on March 17, 2025
Written by Matt McMillen, Hilary Parker
10 min read

Invasive lobular carcinoma (ILC) is a type of breast cancer. It begins in lobules — the cells of the mammary glands that make milk — and spreads to other parts of the breast. It’s the second most common form of breast cancer after invasive ductal carcinoma (IDC), which begins in a milk duct.

It’s different from lobular carcinoma in situ (LCIS) — another type of abnormal cell growth in the breast that stays inside the lobules.

ILC is more likely than other types of breast cancer to be found in both breasts. It can also spread to other areas of your body.

Invasive carcinoma definition

An invasive carcinoma is a cancer that has spread into healthy tissue near where the cancer started. It’s also called infiltrating cancer. When invasive, the cancer becomes more likely to metastasize or spread to other parts of the body, making it extremely difficult to treat.

In breast cancer, invasive carcinomas are those that move beyond the lobules and ducts — where milk is made, stored, and transported — into the tissue area that supports the breast, which contains blood vessels and lymphatic channels.

"When the cancer is able to access these structures, it has a way to spread outside the breast to lymph nodes and other organs," says Megan Kruse, MD, a hematologist and medical oncologist at the Cleveland Clinic Cancer Center in Cleveland, OH. "This is largely what makes cancer dangerous."

Invasive ductal vs. invasive lobular carcinoma

These cancers both develop in the breast, but many things make them different from one another.

Where the cancer begins. IDC starts in the cells lining the milk (or mammary) ducts. These ducts carry milk through the breast to the nipple. Invasive lobular cancer starts in the lobules, where milk is made.

How common the cancer is. IDC is much more common than lobular cancer, making up about 80% of breast cancer diagnoses. Invasive lobular cancer accounts for about 10%-15%.

How likely it is to occur in one or both breasts. Both cancers occur most often in a single breast. However“ILC has a greater predilection for bilaterality, meaning that it’s more likely than IDC to involve both breasts,” says Amy Tiersten, MD, a professor in the Division of Hematology and Medical Oncology and a member of the Breast Cancer Medical Oncology Program at Mt. Sinai in New York City, NY. About 10%-20% of those with ILC have it in both breasts when they’re diagnosed.

How difficult it is to detect. ILC can be trickier to spot than IDC. That’s because the cancer cells tend to grow in a line, spread out over a wide area, rather than clumping together to form a solid mass, or tumor. “This growth pattern can make it appear as a vague finding on imaging, which is sometimes missed on mammogram,” says Carlie Thompson, MD, a breast cancer surgeon and assistant professor of surgery at UCLA Health in Los Angeles, CA. “Instead of a firm, distinct lump, ILC may cause breast firmness, fullness, or changes in texture that feel different from typical breast tissue.”

When it develops. ILC also tends to develop more often after menopause than IDC, Thompson says. The National Cancer Institute estimates that 67% of ILC is diagnosed after age 60, compared with 59% of other types of breast cancer.

Whether it is low grade or high grade. Compared with IDC, invasive lobular breast cancer is more often a low-grade cancer, in which the cancer cells look more like healthy cells than those of a high-grade cancer. Low-grade cancers typically progress more slowly and can have a better prognosis. According to Kruse, though the tumors may be low-grade, they are often bigger at the time of diagnosis.

“[That’s] likely because it takes more time to find them on imaging before diagnosis,” says Kruse.

How likely it is to come back. Generally, both types of cancer — invasive lobular carcinoma and invasive ductal carcinoma — have a similar prognosis.

“However,” says Thompson, “because ILC can be more difficult to detect on a mammogram and may be diagnosed at a later stage, it can sometimes carry a slightly higher risk of recurrence," adding that ILC is more likely than IDC to be driven by the hormones estrogen and progesterone.

“[That] makes it responsive to hormone therapies that can reduce the risk of recurrence over time,” she says.

Lastly, invasive lobular breast cancer is more likely than IDC to recur within 5-10 years after it’s first diagnosed, Kruse says.

Lobular carcinoma in situ

Lobular carcinoma in situ (LCIS) is not cancer. In this condition, abnormal cells that look similar to cancer grow in the breast’s lobules, says Kruse.

Having such cells does indicate a higher risk of developing ILC or IDC during your lifetime. But, Tiersten stresses, LCIS is “a completely different entity. It is not a precursor to breast cancer, and it is certainly not breast cancer.”

If you have LCIS, you may benefit from more frequent breast cancer screenings or treatments that can lower your chances of developing invasive breast carcinoma.

You might not notice symptoms at first. If you do, they can include:

  • Thickening or hardening in the breast (rather than a distinct lump)
  • An area of swelling or fullness
  • A change to the texture of skin on your breast or nipple, such as dimples or an irritated, red, or scaly area
  • A nipple that turns inward
  • Pain in your breast or nipple
  • Unusual nipple discharge
  • A lump under your arm

Experts aren’t sure exactly what causes breast cancer. It happens when cells change and start to grow out of control.

Things that can make ILC more likely include:

  • Age. Your risk goes up with age.
  • Gender. Women and people assigned female at birth are more likely to get it.
  • Lobular carcinoma in situ (LCIS)
  • Use of combination estrogen-progestin hormone replacement therapy after menopause
  • Hereditary diffuse gastric cancer syndrome, a disorder passed down from your parents

Your doctor will start with a physical exam of your breasts and nearby lymph nodes. If they feel any problems such as thickening, hardening, or swelling, you may have tests including:

  • Mammogram. ILC can be hard to spot on a mammogram, which makes X-ray pictures of your breast, because the cancer cells tend to grow in a line rather than in a mass.
  • Ultrasound. It uses sound waves to create images of the inside of your breast. An ultrasound may be better at finding ILC than a mammogram.
  • Biopsy. If they find a suspicious area, your doctor will order a biopsy to check the cells. Most biopsies use a needle to take out a sample of cells from the breast. In some cases, the doctor will remove a larger sample or the entire tumor.
  • CT scan. This is a powerful X-ray that makes detailed pictures inside your body.
  • PET scan. Along with a CT scan, this test can help find cancer in lymph nodes and other areas.
  • MRI. This uses strong magnets and radio waves to make pictures of the breast and tissues and organs inside your body.
  • Bone scan. A radioactive material called a tracer is injected into your arm. It shows up on pictures to tell your doctor whether cancer may have traveled to your bones.

The results of your exams will tell your doctor if you have cancer and whether it’s spread so they can recommend the best treatment options.

Treatment for ILC involves one or more methods. Surgery and radiation therapy are local treatments, meaning they focus on the area of the cancer. Systemic treatments, such as chemotherapy and hormone therapy, target any cancer cells that may have spread.

Invasive lobular carcinoma surgery

Most women with invasive lobular carcinoma have surgery. Depending on the size of your tumor and how much it’s spread, you may have one of two types:

  • Lumpectomy. Your doctor takes only the tumor and some of the tissue around it.
  • Mastectomy. They remove part or all of your breast, with or without nearby lymph nodes and muscle.

Your doctor may take samples from the lymph nodes in your armpits to check for cancer. They might also remove the lymph nodes. These procedures are called sentinel lymph node biopsy and axillary lymph node dissection.

Radiation for lobular breast cancer

High-energy radiation can destroy cancer cells that may remain after surgery. Your doctor may use a machine to deliver the energy from outside your body (external) or insert radioactive seeds or pellets into your body near the area where the cancer was removed (internal).

Chemotherapy for ILC breast cancer

Chemotherapy, or “chemo,” is when your doctor uses one or more medicines to kill cancer cells. You may get them before surgery to shrink a tumor or afterward to destroy any remaining cells. They come in pills that you swallow and in liquid that goes directly into your bloodstream (intravenous, or IV). Drugs that can treat ILC include:

Hormone therapy for invasive lobular carcinoma

ILC cells often have receptors for the hormones estrogen and progesterone. Receptors are special proteins that help the hormones tell cells to grow and divide. Hormone therapy drugs for ILC lower the amount of estrogen in your body or keep it from telling cancer cells to grow. Common ones include:

Hormone therapy can also reduce the risk of your cancer returning. Your doctor may keep you on hormone therapy for 5-10 years— or even longer — to protect against recurrence, says Thompson.

A protein called HER2 can also tell cancer cells to grow. Other medicines target this protein or its receptors.

Treatment side effects

You may notice side effects during or after cancer treatment. For example, chemotherapy can cause:

Radiation may cause:

  • Breast swelling
  • Pain
  • Skin changes, redness, or bruising
  • Fatigue
  • Breast tissue changes
  • Problems breastfeeding
  • Nerve damage
  • Pain and swelling in your arm or chest (lymphedema)
  • Weakened ribs that fracture more easily
  • Fluid in your breast (seroma)

Before you start treatment, talk with your medical team about what to expect. Let them know about any side effects. Some treatments may be available to help you feel better.

Cancer affects everyone differently. Your outlook may depend on things such as how early you’re diagnosed and how well your body responds to treatment.

In general, about 91% of all women with breast cancer live at least five years after diagnosis. While there isn’t much information about specific types of breast cancer, these survival rates are tracked by stage at diagnosis or how far the cancer has spread:

  • Localized (cancer hasn’t spread outside the breast): More than 99% live at least five years
  • Regional (cancer has spread to lymph nodes near the breast): 87% live at least five years
  • Distant (cancer has spread farther in the body): 32% live at least five years

The likelihood of your cancer returning after treatment depends on several factors, including the stage at which it was diagnosed, how fast it developed, how well you responded to treatment, and whether your cancer was hormone-driven. If it does return, it’s most likely to do so within 5-10 years of diagnosis, though it can be decades later, says Kruse.

Invasive lobular carcinoma is the second most common type of breast cancer in the US. It often grows slowly, but it can be hard to detect. That can prevent it from being caught early. Many different types of treatment exist for ILC. The right one for you depends on its stage when diagnosed, your current health, and the type of treatment you prefer.

Where does invasive lobular breast cancer spread first?

“Like other breast cancers, ILC often spreads first to the nearby lymph nodes, particularly those in the armpit, called the axillary lymph nodes,” says Thompson. “From there, it can spread to distant organs. Interestingly, ILC has a unique tendency to metastasize to unusual locations, such as the gastrointestinal tract, ovaries, peritoneum (the lining of the abdominal cavity), and bones.”

Is lobular carcinoma worse than ductal?

In general, both types of cancer have the same prognosis. Some research, says Tiersten, suggests that invasive lobular cancer’s prognosis is slightly worse.

Does invasive lobular carcinoma always come back?

No. In fact, most people who have had breast cancer will not have a recurrence. In ILC, the cancer can come back, mostly within 5 to 10 years, but some may not return for decades, says Kruse. Certain factors help predict your risk. These include the stage at which it was diagnosed, how fast it developed, how well you responded to treatment, and whether your cancer was hormone-driven.

How serious is invasive lobular carcinoma?

Very serious. ILC is a life-threatening disease that requires medical treatment. But it can be cured if diagnosed and treated in its early stages.

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