Lobular Carcinoma

The breast is made up of two main types of tissue: ducts (which carry milk to the nipple) and lobules (the glands that produce milk). Just as ductal carcinoma describes cancers or precancerous changes arising in the ducts, lobular carcinoma refers to those originating in the lobules. The term encompasses a spectrum of conditions, and the specific type — in situ versus invasive — has very different clinical implications.

Lobular carcinoma in situ (LCIS) involves abnormal cells confined within the lobules. Despite the word 'carcinoma,' LCIS is not currently treated as a cancer; it is considered a risk marker indicating elevated lifetime risk of invasive breast cancer in either breast. Invasive lobular carcinoma (ILC), by contrast, occurs when lobular cancer cells break through the lobule walls and infiltrate surrounding breast tissue. ILC is the second most common invasive breast cancer after invasive ductal carcinoma, accounting for roughly 10 to 15 percent of invasive cases.

ILC has some distinctive characteristics that set it apart from ductal cancer. Its cells tend to grow in single file, infiltrating tissue without forming a well-defined mass — which can make it harder to detect on mammography and harder to feel as a lump. It is more likely to be bilateral (occurring in both breasts) than ductal cancer, and it tends to be hormone receptor-positive. MRI is often recommended for women with ILC to better assess the extent of disease, and treatment decisions are made with these unique features in mind.

If you have been told that a biopsy shows lobular changes, it is worth understanding exactly which type: LCIS (a risk marker requiring surveillance and possible risk-reduction strategies) is a very different finding from ILC (an invasive cancer requiring treatment). Asking for this clarification — and what it means for your next steps — is the most important question you can start with.

For women with ILC specifically, knowing that this cancer type may be less visible on standard mammography is reason to ask your radiologist whether additional imaging such as MRI would be valuable in your case. Because ILC is often hormone receptor-positive, hormonal therapies are frequently a central part of treatment, and understanding how those work can help you feel more prepared. As with all breast cancer diagnoses, having a care team that is experienced with lobular carcinoma and will take the time to explain the nuances of your case makes a significant difference.