Ductal carcinoma is a type of breast cancer that involves the growth of cancerous cells in the lining of breast ducts. Most cases of breast cancer in women are some form of ductal carcinoma.

Breasts are composed of lymph vessels, blood vessels and fatty and connective tissue, as well as ducts and lobules, which are glands capable of producing breast milk. The ducts transport milk from the lobules to the nipple. Breast cancer typically occurs in the ducts or lobules.  

Most forms of ductal carcinoma start in the lining of the breast ducts. When ductal carcinoma is identified just in the ducts, it is known as ductal carcinoma in situ (DCIS). In situ is a Latin term meaning “in place,” and indicates the cancer has not spread from the duct lining, through the basement membrane that separates the breast cells from surrounding tissues. DCIS cells have typical features of cancer, but usually remain within the confines of the breast ducts.

If cancer cells in the breast ducts spread through the duct walls and penetrate the basement membrane, the condition is known as invasive, or infiltrating, ductal carcinoma (IDC). From there, the cancer cells can spread, or metastasize, to other parts of the breast and other parts of the body through the lymphatic system, the bloodstream or directly into adjacent tissues.

Although the overwhelming majority of breast cancers occur in women, men can also develop breast cancer. The male breast contains ducts but few lobules. In men, breast cancer may occur within the ducts, but the cancer does not spread to fatty breast tissue or tissues outside of the breast. Most cases of breast cancer in men are invasive ductal carcinomas. DCIS occurs rarely in men.

While some specialists consider DCIS precancerous, others consider it the earliest stage of breast cancer. With the use of mammograms, DCIS is detected much more readily than in previous years. Regardless of the scientific perspective on this issue, DCIS is a condition that requires medical attention.

Overall, the American Cancer Society (ACS) estimates that more than 178,000 women will be diagnosed with invasive breast cancer in 2007, which includes invasive ductal carcinoma. In addition, the ACS estimates that more than 62,000 women will be diagnosed with in situ carcinomas, of which about 85 percent will be DCIS. Most of the 2,030 cases of breast cancer diagnosed in men in 2007 will be ductal carcinomas. After nonmelanoma skin cancers, breast cancer is the most common form of cancer in women. The ACS estimates that more than 40,000 women and 450 men will die from breast cancer in 2007.