Classification of Cancer

Abstract

Tumors can be either benign or malignant. However benign tumors are usually slow-growing extensive masses that compress rather than invade surrounding tissue. Benign tumors are not cancerous, i.e., cells do not extend to other parts of the body. But malignant tumors are cancerous. Cells in these tumors invade nearby tissues and extend to other parts of the body, and when it spreads from one part of the body to another, it is termed as metastasis. Cancers are categorized in two ways depending upon the type of tissue in which cancer originates known as primary site or the position in the body where the cancer first develops. Malignant tumors are generally fast growing which invade surrounding tissue and colonize distant organs extensively. The capacity of tumor cells to separate from the original mass (the primary tumor) and spread to other organs sets up metastasis. There are hundreds of different cancers from histological point of view which are grouped into six major categories:

• Carcinoma is any malignant cancer that originates from epithelial tissues lining the inner or outer surfaces of the body, generally arising from endodermal or ectodermal germ layers during embryogenesis. Carcinomas invade surrounding tissues and organs and may metastasize or spread to lymph nodes and other sites (Witkiewicz et al. 2011). Common malignancies like breast, colon, and lung cancer are categorized as carcinomas.

• Sarcoma is a malignancy that originates from altered cells of mesenchymal origin in bone, muscle, or connective tissue. Thus, malignant tumors found in cancellous bone, cartilage, fat, muscle, or connective tissues are termed as sarcomas. They occur rarely in humans (Baba and Câtoi 2007).

• Leukemia is a neoplastic disease that usually begins in the bone marrow and results in the abnormal development of white blood cells and is generally classified into acute and chronic forms. Additionally it is classified depending upon the type of white blood cells affected by the disease (Isaacs 2009).

• Lymphoma is a kind of blood cell tumor of lymphocytes. It originates in the glands or nodes of the lymphatic system, a network of vessels, nodes, and organs that purify bodily fluids and develop infection fighting white blood cells or lymphocytes (Cupedo et al. 2011).

• Myeloma arises in the plasma cells of bone marrow. Sometimes myeloma cells accumulate in one bone and form a single tumor called plasmacytoma. Yet in other cases, the myeloma cells accumulate in several bones developing many tumors termed as multiple myeloma. It is also known as plasma cell myeloma, myelomatosis, or Kahler’s disease. In myeloma, unusual plasma cells accumulate collectively in the bone marrow and obstruct the production of normal blood cells (Fonseca and Valdez 2002).

• Adenocarcinoma is a cancer of epithelial tissue that has glandular origin, glandular characteristics, or both. They form the part of larger grouping of carcinomas. Carcinoma is just not limited to epithelial or skin or glands but a diversity of other tissues that lines the cavities and organs of the body. Thus invasive ductal carcinoma, the most common form of breast cancer, is adenocarcinoma which does not use the term in its name, but esophageal adenocarcinoma does to distinguish it from the other common type of esophageal cancers, esophageal squamous cell carcinoma, which is not adenocarcinoma. Several of the most common forms of cancer are adenocarcinomas, and the various sorts of adenocarcinomas vary greatly in all their aspects, so that few useful generalizations can be made about them.

• Blastoma arises in embryonic tissue of organs. It is a cancerous tumor that originates from the immature cells that form the basis for an organ’s structure. It occurs in the cells which are undifferentiated, i.e., they have not developed a specific role within the body yet. It usually occurs in childhood and may rarely occur in early adulthood. Though osteoblastoma (blastoma of the bone) is a noncancerous tumor, otherwise most blastomas are cancerous which include nephroblastoma, medulloblastoma, and retinoblastoma (Harada et al. 2006).