ILC Fact Sheet

Facts About Invasive Lobular Carcinoma: A Distinct Subtype of Breast Cancer

Invasive lobular carcinoma (ILC), also known as lobular breast cancer, is the sixth most diagnosed cancer of women in the US. Recent research has highlighted opportunities to better understand this disease and improve the diagnosis, treatment, and follow-up care for thousands of patients with ILC. Learn more with LBCA’s Frequently Asked Questions.

Lobular breast cancer is not a “rare” cancer

An estimated 39,000 new cases of ILC are diagnosed each year. Approximately 450,000 patients in the US are alive today who are either currently receiving treatment or have completed treatment for lobular breast cancer. ILC is the second most common histological subtype of breast cancer, comprising 10% – 15% of all breast cancers, and impacts more women than cancers of the kidney, brain, pancreas, liver, ovaries, or Non-Hodgkin lymphoma. (Adapted 2018 ACS Surveillance Research, SEER)

New Cancer Cases in Women Chart
Reprinted: Fred Hutch News Service

Lobular breast cancer is a distinct subtype of breast cancer

ILC has specific molecular features distinct from ductal breast cancer with its own unique subtypes and variants[1]. The hallmark of ILC is E-cadherin loss.[2]  A better understanding of ILC’s biology and behaviors could open doors to effective targeted therapies.

ILC cells (on the left) form a distinct, single-file pattern that is very different from the more common ductal breast cancer cells (on the right).

Lobular breast cancer presents differently

Histologically, ILC often forms a distinct, single-file pattern rather than the more common “lump.” ILC has differences in presentation and behavior[3]. Symptoms can include hardening of the breast, swelling, changes in the appearance of the breast or nipple, skin changes, or breast pain.

Know the signs and symptoms of lobular breast cancer

ILC may not form a lump, can be harder to feel on a breast exam, and can be harder to see on a mammogram. Sometimes ILC may have not physical symptoms. However, there are some signs and symptoms that are associated with ILC. The graphic below depicts some of these ILC signs and symptoms. If you detect any of these physical changes in your breast, it may be wise to report them to your health care provider. If you have any of these changes but a mammogram is negative, you might want to talk with a doctor about additional imaging or an MRI. It is important to remember that in most cases, these changes are NOT breast cancer. A downloadable pdf of the signs and symptoms of ILC is available here.

infographic showing changes in the breast that might indicate lobular breast cancer

Lobular breast cancer is harder to detect in screening, advanced imaging, and self-exams

Current imaging tools are less reliable for early detection of ILC and detection of distant recurrence. ILC is often not detectable in routine mammogram or other screening leading to later detection and diagnosis when the ILC tumor is at a later stage. Imaging to diagnose local or distant recurrence of ILC can also be inadequate.[4]

New methods for detection are in development to better detect ILC. Some are in clinical trials such as FES PET (18F-fluoroestradiol Positron Emission Tomography) or will be part of future clinical trials such as Contrast Enhanced Mammography. Check back for updates on innovative and more accurate methods for detecting ILC as they are identified.

Lobular breast cancer may respond differently to standard of care treatments

There is increasing evidence that standard of care chemotherapy and endocrine therapies currently equally applied to breast cancer patients may have different effectiveness when applied to ILC and invasive ductal carcinoma (IDC). In some cases, the benefits of chemotherapy for ILC will not outweigh the risks and negative experience of side effects and will not be recommended. There are prognostic tests, such as MammaPrint and Oncotype DX that analyze a sample of a tumor genetic material to determine the likelihood of recurrence. They are used to help make decisions about whether more treatments after surgery would be helpful and for how long.[5] More research is needed to understand further the utility of these tests for predicting the risk of recurrence of ILC, specifically and to refine ILC treatment protocols accordingly.

Lobular breast tumors frequently recur many years after primary diagnosis

While ILC is frequently associated with an excellent initial prognosis, patients can experience late recurrences. There is increasing evidence that long-term outcomes of patients with ILC may be worse than those with IDC.[6]

Lobular breast cancer sometimes has a different metastatic pattern from ductal breast cancer

If you have been diagnosed with lobular breast cancer, it’s important to know where it can metastasize (spread) and the symptoms. Like patients with IDC, people with ILC experience metastases to the bones, lungs, brain, and liver. However, there are also significant differences in metastatic patterns between IDC and ILC, including increased spread of ILC to gastrointestinal, abdominal (peritoneal), and ovarian tissues. ILC can metastasize many years after diagnosis. Report any symptoms you may be experiencing in any of these areas to your oncologist. A printable document on the signs and symptoms of metastatic breast cancer can be downloaded here.


[1] McCart Reed, Breast Cancer Research 2015; Dabbs D, Breast Pathology, Elsevier

[2] Ciriello, Cell 2015

[3] Arpino et al, Breast Cancer Research, 2004; Mathew A et al GebFra 2017

[4]  Johnson, K., Sarma, D. & Hwang, E.S. Lobular breast cancer series: imaging. Breast Cancer Res 17, 94 (2015),Hogan MP, Ulaner GA. J Nucl Med. 2015 Nov;56 (11):1674-80), American Journal of Roentgenology. 2014;202: 1140-1148. 10.2214/AJR.13.11156

[5] Metzger-Filho et al, JCO 2015; Delpech, et al. Br J Cancer 2013 23299541; Barroso-Sousa R, Metzger-Filho O.   Ther Adv Med Oncol. 2016

[6] Pestalozzi et al, JCO, 2008; Engstrom et al, Histopathology, 2015; Adachi et al, BMC Cancer, 2016; Chen et al, PLoS 2017

Updated 2/12/2018

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