4. 1 .2. 2.2. Histological T ypes and V ariants of C arcinoma

Adenocarcinoma : ( adeno = gland) 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.

There are a large number of rare subtypes of anaplastic, undifferentiated carcinoma. Some of the more well known include the lesions containing pseudo-sarcomatous components: spindle cell carcinoma (containing elongated cells resembling connective tissue cancers), giant cell carcinoma (containing huge, bizarre, multinucleated cells), and sarcomatoid carcinoma (mixtures of spindle and giant cell carcinoma). Pleomorphic carcinoma contains spindle cell and/or giant cell components, plus at least a 10% component of cells characteristic of more highly differentiated types (i.e. adenocarcinoma and/or squamous cell carcinoma). Very rarely, tumors may contain individuals components resembling both carcinoma and true sarcoma, including carcinosarcoma and pulmonary blastoma.

4. 1 .2. 2.3. Frequent O rgan S ites of C arcinoma

• Lung: Carcinoma comprises > 98% of all lung cancers.
• Breast: Nearly all breast cancers are ductal carcinoma.
• Prostate: The most common form of carcinoma of the prostate is adenocarcinoma.
• Colon and rectum: Nearly all malignancies of the colon and rectum are either adenocarcinoma or squamous cell carcinoma.
• Pancreas: Pancreatic carcinoma is almost always of the adenocarcinoma type and is highly lethal.

Some carcinomas are named for their or the putative cell of origin, (e.g. hepatocellular carcinoma , renal cell carcinoma ).