Stage 0 breast cancer, or in situ ductal carcinoma (DCIS), occurs when there are abnormal cells in the mammary ducts, but these cells have not spread beyond the canal wall to reach the surrounding tissues, bloodstream, or lymph nodes.

DCIS is noninvasive and is sometimes called "precancerous". However, DCIS has the potential to become invasive.

There are generally no symptoms of stage 0 breast cancer, although it can occasionally cause a lump in the breast or bleeding in the nipple.

The exact cause of stage 0 breast cancer is not clear, but the condition may be more common in people who:

- have a personal history of breast cancer
- have a family history of breast cancer or genetic mutations
- were born after the age of 30 or have never been pregnant
- menstruated before the age of 12
- experienced menopause after the age of 55

Lifestyle factors can increase your chances of having this condition:

- Physical inactivity
- Large body size after menopause
- Alcohol abuse
- Smoking

Sources: Healthline, Women's Health