Lobular Carcinoma in Situ (LCIS)

Lobular carcinoma in situ (LCIS) is a rare condition that happens when you have abnormal cells in your lobules — the glands in your breasts that produce breast milk.

LCIS isn’t breast cancer even though its name includes the term “carcinoma” (cancer). The abnormal cells in your breast glands aren’t cancerous. They’re “in situ,” meaning they don’t become invasive cancer that’s spreading from your lobules to another part of your breast.

Having LCIS doesn’t mean you have a serious illness. But a diagnosis of LCIS does increase the chance that you’ll develop breast cancer later on.

LCIS types

Healthcare providers classify lobular carcinoma in situ by the way abnormal cells appear when viewed under a microscope:

• Classic LCIS: Tests show there are cells lining your lobules that are smaller than normal cells.
• Pleomorphic LCIS: Cells are larger than normal cells and look very different.
• Florid LCIS: Abnormal cells are forming a mass in your lobules. Tests may show an area of dead cells in the middle of the mass.

Is LCIS a common condition?

No, it’s not. It affects between 4 and 11 per 100,000 women and people assigned female at birth (AFAB). It’s even less common in men and people assigned male at birth (AMAB) — 1 in 100,000 people AMAB have LCIS.