Carcinoma

In medicine, carcinoma is any cancer that arises from epithelial cells. It is malignant by definition: carcinomas invade surrounding tissues and organs, and may spread to lymph nodes and distal sites (metastasis). Carcinoma in situ (CIS) is a pre-malignant condition, in which cytological signs of malignancy are present, but there is no histological evidence of invasion through the epithelial basement membrane.

 Classification of carcinoma

 Carcinoma, like all neoplasia, is classified by its histopathological appearance. Adenocarcinoma and squamous cell carcinoma, two common descriptive terms for tumours, reflect the fact that these cells may have glandular or squamous cell appearances respectively. Severely anaplastic tumours might be so undifferentiated that they do not have a distinct histological appearance (undifferentiated carcinoma).

 Sometimes a tumour is referred to by the presumptive organ of the primary (eg carcinoma of the prostate) or the putative cell of origin (hepatocellular carcinoma, renal cell carcinoma). 

Types of lung carcinoma

     * Adenocarcinoma is a malignant tumour originating in the epithelial cells of glandular tissue and forming glandular structures. This is a common in the lung forming 30-40% of all lung carcinomas, found peripherally, arising from goblet cells or type II pneumocytes.

     * Squamous cell carcinoma due to squamous metaplasia. This accounts for 20-30% of lung tumours and is usually hilar in origin. 

    * Small cell carcinoma is almost certainly due to smoking. These metastasise early, and may secrete ADH (lowering patient sodium concentration). 

    * Large cell undifferentiated carcinomas account for 10-15% of lung neoplasms. These are aggressive and difficult to recognise due to the undifferentiated nature. These are most commonly central in the lung.

     * Sinonasal undifferentiated carcinoma

Staging

 The staging of cancers is the extent of spread of the neoplasm. Grading is the system used to record the tumours degree of differentiation from the parent tissue. A high grade shows little differentiation and the prognosis is therefore poor.

Carcinomas, like all cancers, are staged according to the extent of disease. The UICC/AJCC TNM system is often used, however for some common tumours, classic staging methods (such as the Dukes classification for colon cancer) are still used.