Breast cancer. Light micrograph of cells from an adenocarcinoma cancer of the breast. The cells have a chaotic appearance. Adenocarcinoma is a cancer arising from cells lining glandular structures in an organ. Breast cancer is the most common cancer in women. It is usually painless, and is often first detected as a hard lump in the breast. There may also be a discharge from the nipple. If the cancer is detected early, surgical removal can effect a cure. Mammographic (X-ray) screening of women, and regular self-examination of the breasts, can help to detect any cancer early. If the cancer has spread beyond the breast, the prognosis is worse. Magnification unknown.