Invasive Lobular Carcinoma (ILC): Understanding Lobular Breast Cancer
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: Key Facts About Invasive Lobular Carcinoma
Invasive lobular carcinoma (ILC) is a breast cancer making up about 10% to 15% of breast cancers. It often does not form a lump, because cells spread in single-file strands, and it usually grows in response to estrogen. It can spread to unusual areas and recur 10 to 15 years after treatment. Treatment combines surgery, chemotherapy, hormone therapy and radiation.
Feature | Details |
Prevalence | About 10% to 15% of breast cancers; an estimated 31,000 to 46,000 women in the U.S. each year. [1] |
Detection | Often does not form a lump; cells spread in a single-file pattern, forming strands. [1] |
Main driver | Usually grows in response to estrogen. Hormone therapy is used when tests show the cancer is estrogen receptor-positive (ER+). [1] |
Unique risk | Can spread to less common areas such as the digestive system and female reproductive organs, and can appear 10 to 15 years after treatment. [1] |
Outlook | In one study, about 94% of women with stage I to III ILC were alive and cancer-free at five years and about 86% at ten years. [1] |
Primary treatment | A combination that may include surgery, chemotherapy, hormone therapy, radiation and targeted therapy. [1] |
What the research says
ILC has a distinct biology and often needs more careful imaging. A 2024 review explains that ILC is the most common special type of breast cancer, accounting for up to 15% of cases. It is driven by loss of the cell adhesion molecule E-cadherin, which produces a discohesive, single-file growth pattern. Compared with invasive ductal cancer, ILC is more commonly bilateral, is typically estrogen and progesterone receptor-positive and HER2-negative, and requires a more accurate diagnostic examination through imaging. (Corso et al., Semin Oncol, 2024)
MRI adds useful information in ILC. A review of the published literature found MRI sensitivity of 93.3% for ILC. MRI detected additional ipsilateral lesions in 32% of patients, found contralateral lesions only visible on MRI in 7%, and changed surgical management in 28.3% of cases. (Mann et al., Breast Cancer Res Treat, 2008)
ILC spreads to different places than ductal cancer. In a database of 761 patients with metastatic breast cancer (88 with ILC), ILC more often spread to the bone (56.8% versus 37.7%) and gastrointestinal tract (5.7% versus 0.3%) as the first site of distant recurrence. Over the whole course of disease, ovarian (5.7% versus 2.1%) and gastrointestinal (8.0% versus 0.6%) metastases were also more frequent, while lung and liver spread was less common. (Mathew et al., Geburtshilfe Frauenheilkd, 2017)
What Is Invasive Lobular Carcinoma (ILC)?
Invasive lobular carcinoma (ILC) is a type of breast cancer that starts in the milk-producing and transportation system of the breast. Healthcare providers may use the terms "lobules" or "terminal duct lobular units" to describe where this cancer starts. It is called "invasive" because the cancer cells have moved into the surrounding breast tissue. [1]
This type of breast cancer usually grows in response to estrogen, the main female hormone, and it grows slowly. Like all other breast cancers, ILC can spread through breast tissue or to other areas of the body. It affects an estimated 31,000 to 46,000 women in the U.S. each year. Early diagnosis and treatment may cure it, but ILC can spread to other areas of the body many years after diagnosis and treatment. [1]
Most breast cancers form a tumor that may make a lump you can feel. ILC is different. Early on, ILC cells spread out in a single file to form strands or strings of cancer cells. As ILC grows slowly and may not form a lump, it may not cause noticeable changes in your breasts. [1]
Recognizing the Symptoms and Signs
When ILC causes symptoms, they can include: [1]
Breast pain or warmth.
Breast skin that looks or feels thicker than usual, or has dimples, tiny dents or puckers.
Changes in breast size and shape, such as an area of swelling or fullness.
An inverted nipple that points into the breast instead of out.
A lump near the armpit.
Nipple discharge.
Skin discoloration that appears reddish or darker than usual.
Because these changes can be subtle, any new or unusual breast change is worth having evaluated by a healthcare provider. [1]
Causes and Risk Factors
ILC happens when genetic mutations turn healthy cells into cancer cells. Experts are not sure what causes the mutations. Researchers believe the following factors increase the risk of invasive lobular carcinoma: [1]
Being age 55 or older.
Giving birth after age 30 or not giving birth.
Having had breast cancer previously.
Having a family history of breast cancer or ovarian cancer.
Having lobular carcinoma in situ (LCIS).
Inheriting certain genetic mutations.
Starting menopause later than usual (after age 55).
Starting your period earlier than usual (before age 12).
Receiving certain types of hormone therapy for menopause symptoms.
Diagnosis, Staging, and Treatment
A healthcare provider will ask about your symptoms and examine your breasts and the area near your armpits. They may recommend a mammogram to look for abnormal masses, a breast MRI to get very detailed images of breast tissue, and a breast ultrasound to focus on specific areas. A breast biopsy is used to get a small sample of tissue, which a pathologist examines under a microscope for abnormal cells. Test results are used to stage the cancer, from stage I to stage IV, and to plan treatment. Stage IV means the cancer has spread to distant areas such as the lungs, liver or bones. [1]
Treatment may be a combination of: [1]
Breast cancer surgery.
Chemotherapy before or after surgery.
Hormone therapy if tests show you have estrogen receptor-positive (ER+) breast cancer.
Radiation therapy to kill any cancer cells that may remain after surgery.
Targeted therapy, which focuses on the genetic mutations that turn healthy cells into cancer cells.
Recovery depends on the treatment. It can take two to four weeks to recover from breast cancer surgery, and recovering from treatments like chemotherapy may take six months to a year. [1]
The Unique Risk of Metastasis
Breast cancer that spreads typically affects the brain, bones, liver and lungs, and ILC may spread to those areas. But it may also spread to less common areas, including the digestive system (colon, small intestine and stomach), the female reproductive organs (ovaries and uterus), the leptomeninges (the lining of the brain and spinal cord), the peritoneum (the lining of the abdomen) and the tissues around the eye. [1]
ILC can also spread to areas far from the breast 10 to 15 years after diagnosis and treatment, which is why long-term follow-up is important. [1]
Outlook
One study found that overall, 94% of women with ILC were alive and cancer-free five years after their diagnosis, which includes women diagnosed at stage I to stage III, and about 86% were alive and cancer-free 10 years after diagnosis. In general, the earlier the stage at diagnosis, the better the outlook. Five-year survival for ILC is similar to other types of breast cancer, but it is 4% to 10% lower at the 10-year mark. Survival rates are estimates and do not predict how long any one person will live. [1]
Contact your cancer care team if you have signs of a surgical wound infection, such as a fever above 101 degrees Fahrenheit (38.4 degrees Celsius) or thick, cloudy discharge from the incision, treatment side effects stronger than you expected, or pain that prescription pain medication does not ease. [1]
Learn more. For more evidence-based health guides, visit Rinnit.com.
Frequently Asked Questions
Why is ILC harder to find on a mammogram?
ILC cells grow in thin single-file strands and may not form a lump, so you may have ILC for years before it is seen on a mammogram or causes symptoms.
Is ILC more dangerous than other breast cancers?
Five-year survival for ILC is similar to other types of breast cancer, but it is 4% to 10% lower at the 10-year mark. Researchers are working to understand why and to improve long-term outcomes.
What is the "single file" pattern?
The "single file" pattern describes how ILC cells line up in a single row, forming strands or strings of cancer cells, instead of clustering into a solid mass.
What is the role of hormone therapy in ILC?
ILC usually grows in response to estrogen. If tests show your cancer is estrogen receptor-positive (ER+), hormone therapy is part of treatment.
How long does recovery take?
It depends on your treatment. Recovery from breast cancer surgery can take two to four weeks, while recovering from treatments like chemotherapy may take six months to a year.
What is LCIS, and does it raise the risk of ILC?
Lobular carcinoma in situ (LCIS) is listed as a risk factor for invasive lobular carcinoma. Ask your care team what an LCIS diagnosis means for you.
Can ILC affect both breasts?
A 2024 review notes that ILC is more commonly bilateral than invasive ductal cancer, which is one reason it needs careful imaging.
Should I get an MRI?
Discuss your screening plan with your doctor. Breast MRI gives very detailed images and is often used to see the full extent of lobular breast cancer.
Is chemotherapy always needed for ILC?
Not necessarily. Treatment may be a combination of surgery, chemotherapy, hormone therapy, radiation and targeted therapy, depending on your stage and tumor tests.
Who is most at risk?
Being age 55 or older is one of the listed risk factors, along with giving birth after age 30 or not giving birth, a family history of breast or ovarian cancer, a history of LCIS, starting periods before age 12, starting menopause after 55, and certain types of menopausal hormone therapy.
What is stage IV lobular breast cancer?
Stage IV means the cancer has spread to distant areas of the body, such as the lungs, liver or bones.
Can ILC be cured?
Early diagnosis and treatment may cure ILC, but it can spread to other areas of the body many years after diagnosis and treatment, so long-term follow-up matters.
What should I ask my doctor after an ILC diagnosis?
Ask about the size of the cancer, its hormone receptor status, whether it has spread to lymph nodes, and what imaging, such as an MRI, is needed to plan surgery.
Conclusion
Invasive lobular carcinoma presents unique challenges in detection and long-term management because of its strand-like growth and its potential to spread late and to unusual sites. With careful imaging and a personalized treatment plan, many people do well. Paying attention to changes in the skin and texture of the breast, and keeping up with long-term follow-up, are the most important steps. [1]
References
Cleveland Clinic. Invasive Lobular Carcinoma (ILC). Cleveland Clinic. Last updated April 21, 2025. https://my.clevelandclinic.org/health/diseases/21180-lobular-breast-cancer
Corso G, Fusco N, Guerini-Rocco E, et al. Invasive lobular breast cancer: Focus on prevention, genetics, diagnosis, and treatment. Semin Oncol. 2024;51(3-4):106-122. PMID 38897820. https://doi.org/10.1053/j.seminoncol.2024.05.001
Mann RM, Hoogeveen YL, Blickman JG, et al. MRI compared to conventional diagnostic work-up in the detection and evaluation of invasive lobular carcinoma of the breast: a review of existing literature. Breast Cancer Res Treat. 2008;107(1):1-14. PMID 18043894. https://doi.org/10.1007/s10549-007-9528-5
Mathew A, Rajagopal PS, Villgran V, et al. Distinct Pattern of Metastases in Patients with Invasive Lobular Carcinoma of the Breast. Geburtshilfe Frauenheilkd. 2017;77(6):660-666. PMID 28757653. https://doi.org/10.1055/s-0043-109374
Medical disclaimer
This article is for general educational purposes only and is not a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider with any questions about a medical diagnosis or treatment plan.
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