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.



The term carcinoma has also come to encompass malignant tumors composed of transformed cells whose origin or developmental lineage is unknown, but that possess certain specific molecular, cellular, and histological characteristics typical of epithelial cells. This may include the production of one or more forms of cytokeratin or other intermediate filaments, intercellular bridge structures, keratin pearls, and/or tissue architectural motifs such as stratification or pseudo-stratification.

Types and variants of Carcinoma

• Adenocarcinoma: refers to a carcinoma featuring microscopic glandular-related tissue cytology, tissue architecture, and/or gland-related molecular products, e.g., mucin.
• Squamous cell carcinoma: refers to a carcinoma with observable features and characteristics indicative of squamous differentiation (intercellular bridges, keratinization, squamous pearls).
• Adenosquamous carcinoma: refers to a mixed tumor containing both adenocarcinoma and squamous cell carcinoma, wherein each of these cell types comprise at least 10% of the tumor volume.
• Anaplastic carcinoma: refers to a heterogeneous group of high-grade carcinomas that feature cells lacking distinct histological or cytological evidence of any of the more specifically differentiated neoplasms. These tumors are referred to as Anaplastic or Undifferentiated carcinomas.
• Large cell carcinoma: composed of large, monotonous rounded or overtly polygonal-shaped cells with abundant cytoplasm.
• Small cell carcinoma: Cells are usually round and are less than approximately 3 times the diameter of a resting lymphocyte and little evident cytoplasm. Occasionally, small cell malignancies may themselves have significant components of slightly polygonal and/or spindle-shaped cells.

The hallmark of a malignant tumor is its tendency to invade and infiltrate local and adjacent structures and, eventually, spread from the site of its origin to non-adjacent regional and distant sites in the body, a process called metastasis. If unchecked, tumor growth and metastasis eventually creates a tumor burden so great that the host succumbs. Carcinoma metastasizes through both the lymph nodes and the blood.

Carcinomas can be definitively diagnosed through biopsy, including fine-needle aspiration (FNA), core biopsy, or subtotal removal of single node. Microscopic examination by a pathologist is then necessary to identify molecular, cellular, or tissue architectural characteristics of epithelial cells.