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What Is Lobular Breast Cancer?
Invasive lobular carcinoma of the breast (ILC), or lobular breast cancer, is the second most common type of breast cancer, accounting for between 10-15% of all breast cancers. Lobular breast cancer cells tend to grow in “single-file” lines, strands, or sheets through the breast, instead of forming a lump. This growth pattern is due to loss of the gene CDH1 and subsequent absence of the protein E-cadherin, which is seen in ~95% of ILC. The unique growth pattern of ILC makes them more difficult to detect than other breast cancer cells; ILC tend to be larger at diagnosis and may be more likely to have spread to the lymph nodes.
ILC is more likely than other invasive breast cancers to develop into both breasts. According to the American Cancer Society, about 1 in 5 women diagnosed with ILC have the cancer in both breasts at the time of diagnosis.The Lobular Breast Cancer Alliance estimates that over 44,000 ILC cases are diagnosed each year. Most of the women diagnosed with ILC are over 55 years old. While ILC can occur at any age, it is more common in those who are post-menopausal.
Lobular Breast Cancer Prognosis and Survival Rates
When detected and treated early, ILC exhibits a favorable prognosis.ILC survival rates are roughly the same as other breast cancers. Cancer localized to the breast has a 5-year relative survival rate of 99%. Regional cancer that has spread to nearby lymph nodes has a 5-year relative survival rate of 88%. Distant cancer that has spread to other parts of the body has a 5-year relative survival rate of 34%.
If ILC recurs it is often more than 10 years after the primary diagnosis.
Why Come to CU Cancer Center for Lobular Breast Cancer
As the only National Cancer Institute-designated Comprehensive Cancer Center in Colorado and one of only four in the Rocky Mountain region, the University of Colorado Anschutz Cancer Center has doctors who provide evidence based, patient-centered care with specific attention to the nuances of lobular breast cancer care, and researchers dedicated to diagnostic and treatment innovations.
The CU Anschutz Cancer Center is home to a lobular breast cancer research initiative, which brings together an interdisciplinary team engaged in cutting-edge basic, translational, and clinical research for patients with ILC. The Lobular Breast Cancer Initiative puts Colorado at the forefront of precision cancer care for patients facing ILC through innovation, discovery, and collaboration.
There are multiple breast cancer clinical trials being offered by CU Anschutz Cancer Center members at any time.
à An Understudied Type of Breast Cancer Poses a Lurking Threat
Types of Lobular Breast Cancer
There are different types of invasive lobular carcinoma (ILC):
- Classic – Classic invasive lobular carcinomas are slower-growing, hormone receptor (HR) positive cancers. The classic ILC is unlikely to make extra HER2 (human epidermal growth factor receptor 2), a protein that controls how healthy cells grow and divide. This ILC tends to grow in thin lines or strands.
- Solid – Solid ILC grows in large sheets, with minimal connective tissue between them.
- Alveolar – Alveolar ILC is a rare type of ILC that grows in clusters.
- Tubulolobular – Tubulolobular ILC cells grow in a combination of the classic single-file lines and cells that form hollow, tubular structures.
- Pleomorphic - Pleomorphic ILCs are typically quicker-growing. The pleomorphic type is often HR positive and HER2-negative. Invasive pleomorphic lobular carcinoma is a very rare and distinct variant, characterized by variations in the size and nuclei of the cancer cells, according to a study in the Journal of Breast Cancer.
Causes of Lobular Breast Cancer
Genetic changes in the DNA affecting the presence and function of the epithelial protein E-cadherin. The exact underlying causes of ILC are unknown, but there are genetic, lifestyle, and environmental risk factors for developing this cancer.
Risk Factors of Lobular Breast Cancer
The risk factors for lobular breast cancer are similar to the risk factors for breast cancer in general. Factors that may raise the risk include:
- Family or personal history of breast cancer.
- Personal history of breast conditions.
- Beginning period at a younger age (<12).
- Beginning menopause at an older age (<55).
- Dense breast tissue.
- Alcohol consumption.
- Having your first child over the age of 30.
- Having never been pregnant.
- Inherited DNA changes.
- Menopausal hormone therapy.
- Older age.
- Obesity.
- Radiation exposure.
Symptoms of Lobular Breast Cancer
Lobular breast cancer or invasive lobular carcinoma (ILC) may not cause noticeable symptoms in its early stages. Unlike some other breast cancers, ILC does not always form a distinct palpable mass. Instead, a person may notice an area of fullness, firmness, thickening in the breast or maybe nothing at all. Other signs of ILC can be similar to those associated with other forms of breast cancer.
Possible signs and symptoms of invasive lobular carcinoma include:
- Thickening in the breast that feels different from the surrounding tissue.
- Nipple appears flattened or inverted.
- Change in shape, size, or appearance of the breast:
- One breast appears larger than the other.
- Skin dimpling or irritation.
- Changes to the skin over the breast, which can include peeling, scaling, crusting, redness, or flaking skin on the breast.
- Changes in breast skin color.
- Breast or nipple pain.
Diagnosing Lobular Breast Cancer
Diagnosing ILC can be more difficult than other breast cancers because the cells tend to grow along tissue planes rather than a distinct mass. Usually, a diagnosis involves a breast exam, mammogram, ultrasound, sometimes MRI, and tissue biopsy.
Following a diagnosis, additional tests provide more information about the cancer – receptor status of the cancer cells and imaging to see if the cancer has started outside of the breast. Most lobular breast cancers are hormone receptor-positive, which means estrogen or progesterone can promote the cancer cells growth.
Stages of Lobular Breast Cancer
The stage of ILC is determined by the size of the cancer in the breast and if it has spread into the axillary lymph nodes or throughout the body. Axillary staging is usually determined with an axillary ultrasound and sentinel lymph node biopsy, which is performed at the time of surgery. Systemic staging can be determined by CT scan, brain MRI, PET-FDG scan and also PET-FES. Staging work-up is not always performed on every ILC diagnosis; generally, it is only if the primary cancer is larger or of it has spread into the lymph nodes.
- Stage 1: The ILC is small, less than 2 centimeters. It has not spread to axillary lymph nodes, or only a couple cells are found in the lymph nodes.
- Stage 2: The ILC is between 2 and 5 centimeters with or without spread into axillary lymph nodes.
- Stage 3: The ILC is large (over 5 centimeters) and has widely spread to axillary lymph nodes and clavicular lymph nodes.
- Stage 4: Metastatic. The ILC has spread to other areas of the body, commonly to the liver, lungs, brain, and sometimes within the abdomen.
Treatments for Lobular Breast Cancer
Treatment for ILC is currently based on broader guidelines for all breast cancers, taking into consideration hormone receptor and HER2 status, stage, grade and related factors. Ongoing research, including through the Lobular Breast Cancer Initiative at CU, is working to tailor treatment to the distinct biology and clinical behavior of ILC.
Surgery:
- Breast surgery (lumpectomy or mastectomy): A lumpectomy surgery removes the cancerous tumor and preserves the surrounding normal, healthy breast tissue. This surgery is typically an option when the primary breast tumor is small. Mastectomy is removal of the entire breast and is sometimes necessary in order to excise all of the cancer cells.
- Axillary surgery (sentinel lymph node biopsy or axillary lymph node dissection): Sentinel lymph node biopsy is removal of 1-3 lymph nodes in the armpit to determine if the cancer has started to spread. If the cancer is found in 3 or more lymph nodes then a complete axillary lymph node dissection, or removal of all remaining axillary lymph nodes, may be necessary to ensure no cancer cells remain in the region.
Radiation therapy:
A treatment using high-energy rays to destroy cancer cells, often used after a lumpectomy and sometimes also following mastectomy.
Chemotherapy:
A treatment using oral or intravenous drugs to destroy cancer cells. Chemotherapy treatment is determined based on features of the ILC including receport status, genomic alterations and whether or not it has spread throughout the body.
Hormonal therapy:
A treatment using hormone-blockers (against estrogen and progesterone) to lower hormone levels and/or block their function on tumor cells. Hormone receptor positive ILC patients often receive hormonal therapy after surgery and radiation.
Targeted therapy:
A treatment using drugs directly targeted at the proteins in cancerous cells to stop or slow cell growth. For ILC, this typically targets the HER2 receptor, and may include targeting the CDK4/6, PI3K, or AKT proteins.
Immunotherapy:
Typically used for Stage 4/metastatic ILC, this treatment uses the patient’s immune system to fight against the cancer.
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Information reviewed by Lauren Gamble, MD, and Matthew Sikora, PhD, in October 2026.