Lobular Carcinoma in Situ

April 10, 2025

This page was reviewed under our medical and editorial policy by Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Lobular carcinoma in situ, or LCIS, is a rare breast condition that is usually detected by chance during tests done for other reasons. Because of that, it is hard to know exactly how common LCIS is overall. It is estimated to affect about 4 in 100,000 women, and LCIS is found in up to 2.5% of all breast biopsies.

What Is Lobular Carcinoma in Situ?

LCIS is a noncancerous condition in which abnormal cells grow in the lining of the breasts’ milk-producing glands (lobules). It usually does not cause a breast lump or other abnormalities that are visible on a mammogram. Instead, LCIS is typically found when someone undergoes a breast biopsy for another reason. While LCIS is not cancer, it does raise the risk of developing breast cancer in the future. Women diagnosed with LCIS have a 7 to 12 times greater risk of breast cancer than those without the condition.

What Is Lobular Carcinoma?

LCIS rarely spreads beyond the lobule. It differs from a disease known as invasive lobular carcinoma, a form of cancer that spreads from the milk glands into the breast tissue. About 10% of all breast cancers are invasive lobular carcinomas.

What Does in Situ Mean?

The term “in situ” means “in its original place,” so carcinoma in situ refers to abnormal cells that remain in the place where they arise.

Types of LCIS

There are three types of LCIS, depending on the appearance of the abnormal cells lining the lobules.

Classic LCIS: The cells are relatively small and look uniform in size.

Pleomorphic LCIS: The cells are larger and have a more abnormal appearance.

Florid LCIS: The cells are large enough to form a mass, often with some dead cells in the center.

Both florid and pleomorphic LCIS may sometimes be seen on a mammogram.

LCIS Versus DCIS

While LCIS is not cancer, it signals an increased risk for breast cancer in either the breast with or without LCIS, and in rare cases, LCIS may progress to cancer in the affected breast if left untreated.

Some people with LCIS go on to develop ductal carcinoma in situ, or DCIS, which is considered early breast cancer (sometimes called Stage 0 breast cancer).

In DCIS, cancer cells are in the lining of milk ducts, but they have not spread into nearby breast tissue. DCIS is described as a noninvasive or preinvasive form of breast cancer.

Some patients with LCIS may also go on to develop other, more aggressive forms of breast cancer, such as invasive lobular cancer or invasive ductal carcinoma. Regular breast cancer screening often leads to diagnosis in earlier stages when it may be more treatable.

LCIS Treatment

LCIS often requires no treatment. In some cases, though, the doctor might recommend that it be removed to make sure the LCIS is the only abnormality present. This may be done with surgery, such as excisional biopsy, which aims to remove the abnormal cells and as little normal breast tissue as possible.

Whether LCIS is treated or not, doctors recommend that women with the condition have regular follow-ups to detect breast cancer early should it arise. Along with yearly mammograms, that may include office visits for a clinical breast exam or additional imaging tests, such as magnetic resonance imaging (MRI) of the breast.