Breast Anatomy

The mammary gland consists of several lobes and corresponding milk ducts.

Inside the breast

Ductal carcinoma in situ (DCIS)

DCIS is common; every year, over 60,000 women in the US are diagnosed with DCIS.

DCIS occurs when abnormal cells grow inside the milk ducts of the breast. The cells do not go into (or invade) the surrounding tissue, so we call this a non-invasive breast tumor.

Normal duct

DCIS duct

Not all DCIS are the same. We distinguish between different subtypes based on how the cells look, and whether they express hormone receptors:

Nuclear Grade

Pathologists classify DCIS based on nuclear grade, or how normal or abnormal the cells are (nuclear abnormalities). Grade 1 is low, meaning the tumor cells are similar to normal breast cells. Grade 2 is intermediate, and grade 3 is high, meaning the cells are more abnormal and potentially, more aggressive.

Hormone Receptors

Another important factor is whether the DCIS cells have receptors for the hormones estrogen (ER) and progesterone (PR). If the cells in a tumor have ER receptors, the tumor is called ER-positive. Similarly, if the cells have PR receptors, the tumor is called PR-positive. DCIS tumors that are either ER-positive or PR-positive (or both) can potentially be treated with endocrine therapy, also called hormone therapy, which involves a daily pill.

Two Possible Courses of DCIS Without Treatment

DCIS

Becomes invasive cancer (10-20% of cases)

The abnormal cells spread into the surrounding breast tissue and become invasive breast cancer. Unlike DCIS, invasive breast cancer can spread (metastasize) to other parts of your body.

In most women, the transition from DCIS to invasive breast cancer takes several years.

Remains DCIS (80%-90% of cases)

The abnormal cells stay in the breast ducts and you will not have any further symptoms, even if you do not receive any treatment.