What Is Granulomatous Mastitis?

Granulomatous Mastitis (GM) is a rare, benign inflammatory breast condition. It causes firm masses, pain, swelling, redness, and sometimes abscesses that drain through the skin. Because it can look almost identical to breast cancer on imaging, a biopsy is usually needed to confirm the diagnosis.

Who gets GM?

GM most often affects women of reproductive age, especially within a few years of pregnancy or breastfeeding. Reported cases span nearly every ethnicity, but it appears more frequently in women of Hispanic, Middle Eastern, and South Asian descent.

What causes it?

The honest answer is: we're still learning. Current theories include an autoimmune reaction, a slow-growing bacterial component (particularly Corynebacterium kroppenstedtii), hormonal changes, trauma, and a genetic predisposition. It's likely more than one of these factors combined.

How is it different from cancer or a simple infection?

• It's not cancer. GM is benign — but it can look like cancer on imaging and exam, which is why biopsy matters.
• It's not a typical breast infection. Standard antibiotics often fail because the bacteria involved may need special cultures and lipophilic antibiotics.
• It comes back. Recurrence is common, which is why long-term care and a knowledgeable physician matter.

What now?

If you were just told you might have GM, the most useful next steps are: confirm the diagnosis with a biopsy, find a physician who has treated GM before, and give yourself permission to move slowly. GM is scary, but it is treatable — and you're not alone.