4.1.2.2. Carcinoma

Carcinoma is the medical term for the most common type of cancer occurring in humans. Put simply, a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that generally arises from cells originating in the endodermal or ectodermal germ layer during embryogenesis. More specifically, a carcinoma is tumor tissue derived from putative epithelial cells whose genome has become altered or damaged to such an extent that the cells become transformed, and begin to exhibit abnormal malignant properties.

4. 1 .2. 2.1. Pathogenesis of C ancer

Cancer occurs when a single progenitor cell accumulates mutations and other changes in the DNA, histones, and other biochemical compounds that make up the cell's genome. The cell genome controls the structure of the cell's biochemical components, the biochemical reactions that occur within the cell, and the biological interactions of that cell with other cells. Certain combinations of mutations in the given progenitor cell ultimately result in that cell (also called a cancer stem cell) displaying a number of abnormal, malignant cellular properties that, when taken together, are considered characteristic of cancer, including:

• the ability to continue to divide perpetually, producing an exponentially (or near-exponentially) increasing number of new malignant cancerous "daughter cells" (uncontrolled mitosis);
• the ability to penetrate normal body surfaces and barriers, and to bore into or through nearby body structures and tissues (local invasiveness);
• the ability to spread to other sites within the body (metastasize) by penetrating or entering into the lymphatic vessels (regional metastasis) and/or the blood vessels (distant metastasis).

If this process of continuous growth, local invasion, and regional and distant metastasis is not halted via a combination of stimulation of immunological defenses and medical treatment interventions, the end result is that the host suffers a continuously increasing burden of tumor cells throughout the body. Eventually, the tumor burden increasingly interferes with normal biochemical functions carried out by the host's organs, and death ultimately ensues.

Malignant neoplasms are exceptionally heterogeneous entities, reflecting the wide variety, intensity, and potency of various carcinogenic promoters. To date, no simple and comprehensive method for classifying them has yet been devised and accepted within the scientific community. Traditionally, however, malignancies have generally been classified into various taxa using a combination of criteria, including:

One commonly used classification scheme classifies these major cancer types on the basis of cell genesis, specifically:

1. Their (putative) cell (or cells) of origin
1. Epithelial cells => carcinoma
2. Non-hematopoietic mesenchymal cells => sarcoma
3. Hematopoietic cells

• bone marrow -derived cells that normally mature in the bloodstream => Leukemia
• bone marrow -derived cells that normally mature in the lymphatic system => Lymphoma

  4. Germ cells => Germinoma

Other criteria that play a role in a cancer diagnosis include:

• The degree to which the malignant cells resemble their normal, untransformed counterparts
• the appearance of the local tissue and stromal architecture
• the anatomical location from which tumors arise
• genetic, epigenetic, and molecular features