Causes

It's not clear what causes LCIS. LCIS begins when cells in a milk-producing gland (lobule) of a breast develop genetic mutations that cause the cells to appear abnormal. The abnormal cells remain in the lobule and don't extend into, or invade, nearby breast tissue.

If LCIS is detected in a breast biopsy, it doesn't mean that you have cancer. But having LCIS increases your risk of breast cancer and makes it more likely that you may develop invasive breast cancer.

The risk of breast cancer in women diagnosed with LCIS is thought to be approximately 20 percent. Put another way, for every 100 women diagnosed with LCIS, 20 will be diagnosed with breast cancer and 80 won't be diagnosed with breast cancer. The risk of developing breast cancer for women in general is thought to be 12 percent. Put another way, for every 100 women in the general population, 12 will be diagnosed with breast cancer.

Your individual risk of breast cancer is based on many factors. Talk to your doctor to better understand your personal risk of breast cancer.