Introduction to Ductal Carcinoma in Situ

The female breast is made up of glands that produce and release milk after childbirth. The glands that make the milk are called lobules and the tubes that connect them to the nipple are called ducts. The breast itself is made up of lobules, ducts, and fatty, connective, and lymphatic tissue.

Lymph is a clear fluid that contains immune system cells. The fluid is carried in lymphatic vessels that lead to small, pea-sized collections of tissue called lymph nodes. Most lymphatic vessels of the breast lead to lymph nodes under the arm called axillary lymph nodes.

There are several types of tumors that can occur in the breasts. Most are benign (non-cancerous) and are related to fibrocystic changes. Cysts are fluid-filled sacs and fibrosis refers to the forming of connective tissue or scar tissue. Benign breast tumors are abnormal growths, but they do not appear outside of the breast and they are not life threatening.

Breast cancer is the most common cancer among women, other than skin cancer. It is the second leading cause of cancer death in women after lung cancer. Fortunately, deaths from breast cancer have declined significantly, which is though to be due to better detection and improved treatment.

Ductal carcinoma in situ (DCIS) of the breast is an early, localized (limited to a specific area) cluster of cancer cells that start in the milk passages (ducts) but have not penetrated the duct walls into the surrounding tissue. The term "in situ" refers to a tumor that has not spread beyond the place where it originally developed. By definition, DCIS is a non-invasive form of breast cancer because the cancer cells are confined to the milk ducts of the breast.

Ductal carcinoma in situ is sometimes described as "pre-cancerous", "pre-invasive", "non-invasive", or "intraductal carcinoma". Although, by definition, DCIS is an early, localized, non-invasive form of breast cancer, if left untreated, DCIS may progress to 'true' breast cancer by spreading into and invading the surrounding healthy breast tissue. Because doctors cannot predict with any degree of certainty whether DCIS will develop into invasive breast cancer, early diagnosis and treatment is crucial. With appropriate treatment, the prognosis (outlook) for women with DCIS is excellent.

Fortunately, DCIS can often be detected on screening mammography before any symptoms develop. Ductal carcinoma in situ usually appears on mammography as an area of microcalcification (groups of small calcifications clustered together within the breast). With the increased availability of mammography, breast cancers are being detected earlier.

The incidence of DCIS has increased dramatically since the introduction of widespread screening mammography. In 1983, approximately 5,000 cases of DCIS were reported, however, due to the widespread use of screening mammography, approximately 50,000 cases of DCIS are now diagnosed in the United States each year.

Ductal carcinoma in situ represents 10-15% of all new breast cancers diagnosed in the United States and accounts for 30-50% of cancers detected by screening mammography in women less than age 50 years and 15-25% in women over age 50. It also comprises approximately 7-10% of all breast biopsies.