Invasive Lobular Carcinoma (ILC)

How ILC differs from ductal cancer

The single-file growth happens because ILC cells usually lack E-cadherin, a protein that holds cells together.

Lobular carcinoma in situ (LCIS) is different: abnormal cells confined to the lobules, which is not cancer but a marker of higher breast cancer risk in both breasts.

Symptoms

• a thickened, hardened or full area of the breast
• a change in breast size or shape
• dimpling or puckering of the skin
• a newly inverted nipple
• swelling in the armpit
• a palpable lump (less often than with ductal cancer)

Many ILCs are found on screening imaging without any symptoms.

Risk factors

• older age (median age at diagnosis is a few years older than for ductal cancer)
• female sex
• hormone therapy with estrogen plus progestin after menopause
• dense breasts
• LCIS or atypical lobular hyperplasia
• family history, and gene variants such as CDH1 (also linked to hereditary diffuse gastric cancer), BRCA2, PALB2 and CHEK2; see BRCA mutation
• alcohol and early periods or late menopause

Diagnosis

1. Clinical breast exam.
2. Diagnostic mammogram and ultrasound. ILC may appear as subtle distortion rather than a mass.
3. Breast MRI: often recommended to measure the true extent and check the other breast, because ILC is frequently larger than it appears on mammograms.
4. Core needle biopsy: confirms the diagnosis and tests hormone receptors (ER, PR) and HER2.
5. Staging: lymph node evaluation and, for larger tumors, scans for spread.
6. Genetic counseling and testing for those with a strong family history or young age at diagnosis; see genetic counseling.

Treatment

Treatment is planned by a multidisciplinary team and depends on stage, receptors and personal factors.

Surgery

• Lumpectomy (breast-conserving surgery) followed by radiation, when the tumor can be removed with clear margins. Because ILC spreads diffusely, re-excision is needed more often than with ductal cancer.
• Mastectomy with or without reconstruction, for larger or multifocal tumors or by preference.
• Sentinel lymph node biopsy to check the armpit nodes.

Radiation

Usually given after lumpectomy and sometimes after mastectomy.

Endocrine (hormone) therapy

The cornerstone for most ILC, because it is usually ER-positive:

• aromatase inhibitors (letrozole, anastrozole, exemestane) for postmenopausal women
• tamoxifen, or ovarian suppression plus an aromatase inhibitor, for premenopausal women
• typically taken for 5 to 10 years
• CDK4/6 inhibitors (abemaciclib or ribociclib) are added for some higher-risk early cancers and for advanced disease

Chemotherapy and targeted therapy

ILC tends to respond less to chemotherapy than ductal cancer. Genomic tests such as Oncotype DX help decide who benefits. HER2-positive ILC (uncommon) receives HER2-targeted drugs.

Outlook

Outlook depends mostly on stage. Early-stage ILC has high survival rates, similar to or better than ductal cancer in the first years. ILC can recur late, more than 10 years after diagnosis, so long-term follow-up and adherence to hormone therapy matter. Recurrences may appear in unusual places such as the digestive tract or abdominal lining, causing bloating, early fullness or changes in bowel habits.

Frequently asked questions

What is invasive lobular carcinoma?

It is a type of breast cancer that starts in the lobules, the milk-producing glands, and spreads into nearby breast tissue. It is the second most common type of invasive breast cancer and is usually hormone receptor-positive.

What are the symptoms of lobular breast cancer?

ILC often causes a thickening, hardening or fullness in part of the breast rather than a distinct lump. Other signs include changes in breast size or shape, skin dimpling, an inverted nipple or armpit swelling. Many are found on screening without symptoms.

Why is lobular carcinoma hard to detect?

ILC cells grow in thin, single-file lines rather than forming a dense mass, so they may not show clearly on mammograms or feel like a lump. Breast MRI is often used to assess its full size once it has been diagnosed.

Is lobular breast cancer more aggressive than ductal?

Not usually. ILC is often slower-growing and hormone receptor-positive, and early-stage outlook is generally good. However, it can be larger at diagnosis, more often affects both breasts, and can recur many years later in unusual sites.

How is invasive lobular carcinoma treated?

Treatment usually includes surgery (lumpectomy with radiation or mastectomy), lymph node evaluation and hormone therapy for 5 to 10 years. Some patients also receive CDK4/6 inhibitors, chemotherapy or HER2-targeted therapy depending on the tumor's features and stage.