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Most people know that stages of cancer range from Stage 1 to Stage 4, where Stage 4 is considered advanced cancer that has spread to other organs. But when it comes to breast cancer, there’s also an early-stage form of breast cancer called Stage 0.

“In Stage 0 breast cancer there are abnormal cells in the breast tissue — either in the milk ducts or breast lobules — but the cells haven’t spread to healthy tissue,” said Portia Siwawa, M.D., breast cancer surgeon at Geisinger.

There are two types of Stage 0 breast cancer: ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). DCIS and LCIS are considered non-invasive because abnormal cells have not spread from their origin.

Ductal carcinoma in situ (DCIS) is an early form of cancer where abnormal cells are found in the milk ducts, but nowhere else. DCIS is very treatable and is not life threatening, but having DCIS increases the risk for other invasive types of breast cancer.

Many people who have Paget’s disease of the nipple – a rare condition where abnormal cells are found in or around the nipple – also have DCIS or an invasive form of cancer.

Lobular carcinoma in situ (LCIS) is when abnormal cells develop in the breast lobules, the glands that make milk. Though the name includes the word carcinoma, it’s not truly breast cancer.

DCIS and LCIS may not present symptoms. DCIS is typically diagnosed through a mammogram, while LCIS is sometimes not detected through a mammogram. Instead, it is often found after a biopsy or test is conducted for another abnormality.

LCIS does not require treatment, but rather close monitoring to detect breast cancer through mammograms, breast self-exams and other types of imaging tests like an MRI. Depending on whether you’ve been through menopause yet or not, your doctor may also prescribe medication that can help prevent breast cancer from developing.

“Hormonal therapy medicines can help reduce the risk of breast cancer developing because LCIS is often hormone-receptor positive, which means that estrogen or progesterone can promote abnormal cell growth,” said Dr. Siwawa.

Unlike LCIS, DCIS typically requires treatment. One treatment for DCIS is a lumpectomy, where the abnormal cells are removed from the breast but most of the breast is preserved. This is sometimes followed by radiation treatment.

Another option is a mastectomy, where the entire breast is surgically removed. Following surgery, your doctor may also prescribe hormone-blocking medication to prevent abnormal cells from growing again if the DCIS is found to be hormone-receptor positive.

“Unlike invasive cancers, DCIS is not typically treated with chemotherapy because the cancer is limited to one area of the breast and hasn’t spread throughout,” said Dr. Siwawa.

After treatment concludes, your doctor may recommend that you continue taking medication for up to five years to prevent breast cancer.

The outlook for patients diagnosed with Stage 0 breast cancer is typically good. The five-year survival rate is close to 100 percent.

“Treating DCIS and monitoring DCIS or LCIS gives women the best chance of finding invasive breast cancer early and deciding on treatment options,” said Dr. Siwawa.