Carcinomas and sarcomas, as well as mixed forms of cancer and cancer without tumor formation, represent different types of breast cancer. Classifying breast cancer cells involves microscopic evaluation, determining the characteristics of the cells. Cancer cells are either invasive, non-invasive or pre-invasive, states the American Cancer Society.
Non-invasive cancer cells do not spread, or metastasize, to surrounding tissue. However, pre-invasive cancer cells are non-invasive cancer cells with the potential for invasion into other areas. Invasive cancer cells grow into surrounding areas, but in rare cases, a tumor does not grow at all, explains the American Cancer Society.
Carcinomas usually originate in the epithelial cells, which are organ linings found in the breast. Frequently, breast cancer is adenocarcinoma, or a carcinoma originating in glandular tissue. Sarcomas develop in the connective, fat or muscle tissue, according to the American Cancer Society.
As of 2015, the most common type of breast cancer is invasive ductal carcinoma, originating in the milk ducts of the breast. Another common type is ductal carcinoma in situ, a non-invasive cancer with cells resembling cancer cells. A less common type of breast cancer is inflammatory breast cancer, which affects the physical appearance of the breast. Although inflammatory breast cancer resembles the appearance of an orange, the condition comes from blocked lymph vessels, notes the American Cancer Society.