Cancer Stat Facts: Invasive Lobular Carcinoma

At a Glance

In 2024, it is estimated that there are 310,720 new cases of female breast cancer in the United States. Among these newly diagnosed breast cancer cases, 10%-15% are diagnosed as invasive lobular carcinoma.

Percent of New Cases by Age Group: ILC as Compared to Non-lobular

67% of all new lobular diagnoses are in women over the age of 60, while 59% of non-lobular diagnoses occur in women over the age of 60.

Percent of New Cases by Receptor Status at Diagnosis: Lobular Compared to Non-lobular

89% of all new cases of lobular breast cancer are HR+/HER-2-, while 67% of non-lobular carcinomas are HR+/HER-2-.

Invasive Lobular Carcinoma (ILC) Breast Cancer Type

ILC tumors do not usually form in lumps and are hard to image with screening tests or to feel in self-exams.

The hallmark of lobular breast cancer is the lack of the protein E-cadherin³, which helps cancer cells adhere to each other. Because E-cadherin is absent in ILC, ILC tumor cells typically grow diffusely in unconnected lines, throughout the breast without distorting the surrounding structures or forming a lump. This makes them extremely hard to detect on mammograms and ultrasound, especially in women with dense breast tissue, or to visualize elsewhere in the body if metastasized. It also makes even large ILC tumors hard to feel. Symptoms of ILC tumors can range from none to changes in the appearance of the nipple or breast, such as dimpling, hardening of the breast, swelling, or pain.^7,8 On self-examination, ILC often does not feel like a lump but can sometimes be felt as a firmness or mass.

ILC tumors are often diagnosed when they are already over 2cm.

Because the tumors are harder to image and feel, lobular breast cancer is often only diagnosed once tumors are larger than 2cm and later stage, and sometimes already metastatic. Unfortunately, because many clinical trials for treatments require that participants have measurable disease (i.e., meaning the tumor can be imaged and its changes clearly measured), since most ILC tumors are not measurable, lobular breast cancer patients are often not eligible for clinical trials. As a result, there have been extremely few clinical trials to-date focused specifically on ILC and almost none on metastatic lobular breast cancer worldwide.

Lobular breast tumors frequently recur many years after primary diagnosis.

Many scientific studies have confirmed that lobular breast cancer is a distinct breast cancer type and that it behaves differently from the more common non-lobular breast cancers. Recent literature shows significant differences in presentation, response to therapy and outcomes between ILC and NST⁹. For one, while lobular breast cancer, like IDC/NST, can recur any time after initial diagnosis, studies show that ILC often recurs later than IDC, more than 10 years after the initial diagnosis of cancer.¹⁰ In early studies it was suggested that an ILC diagnosis suggested a better prognosis than NST but more recently there are many conflicting studies and some suggesting that the prognosis for ILC was better than that for NST in the first 5 years after diagnosis, but after 10–15 years, ILC patients seemed to have worse prognoses.¹¹ One cause of the conflicting findings relate to the fact that ILC also has many subtypes with potentially many different prognoses associated with each. It is important that more research is conducted on ILC subtypes.

Lobular breast cancer can metastasize to unusual places.

Like IDC/NST, ILC can metastasize to the bones, brain, liver, and lungs. However, ILC can also spread to unique sites such as the gastrointestinal tract (stomach, small intestine, and colon), gynecological organs (ovaries, uterus), the peritoneum (abdominal lining), and in rarer cases leptomeninges (lining of the brain and spinal cord)¹² and orbital tissues (i.e., around the eye).¹³

ILC is currently treated like the more common IDC/NST despite its differences.

Though ILC is hardly a rare cancer, at 15% of breast cancers, for decades, in part because of the smaller numbers of patients at any one site and the insufficient standardization of the diagnosis for pathologists and radiologists, there has been very little research. The standard of care for early-stage hormone receptor positive ILC is the same as treatment of hormone receptor positive non-lobular tumors. More research is needed to identify ILC-specific treatment protocols.¹⁴

Invasive Lobular Carcinoma, a Distinct and Special Type of Breast Cancer – Data Analysis

ILC is currently identified using histology codes. These codes are ascribed once a pathologist examines tissue from surgery or a biopsy under a microscope. The three ICD-0-3 codes (histology codes) which identify ILC include 8520/3: lobular carcinoma, NOS; 8522/3: infiltrating ductal and lobular carcinoma; and 8524/3: infiltrating lobular mixed with other types of carcinomas).

Invasive lobular carcinoma (ILC) and ILC mixed type, as defined in the data using the above-mentioned histology codes are all considered invasive carcinomas. Lobular Carcinoma in Situ (LCIS) is not invasive and is not considered a cancerous lesion. It has been excluded from the information. DCIS, which is also not an invasive form of cancer is excluded from the comparison analysis. It should also be noted that incidence of males with lobular breast cancer are extremely rare, less than .1%. Therefore, the analysis focuses only on incidences of breast cancer in females.

To identify where there are differences, the data on invasive lobular carcinoma are compared to all other invasive breast cancers (identified as non-lobular).

Related Stat Facts

• Female Breast Cancer Stat Facts
• Female Breast Cancer Subtypes Stat Facts

Footnotes

Suggested Citation

All material in this report is in the public domain and may be reproduced or copied without permission; citation as to source, however, is appreciated.

SEER Cancer Stat Facts: Invasive Lobular Carcinoma. National Cancer Institute. Bethesda, MD, https://seer.cancer.gov/statfacts/html/ilc.html