Precancerous Lesions – Early Warning Signs Of Cancer
A precancerous condition is one which can be recognized by either clinician or pathologist and which idicates that the bearer has a substantially greater risk of developing a malignant tumor than normal. The early stages of precancerous change (which presumably indicate the occurrence of the earlier mutations of a multistage conversion to malignancy) can often be recognized histologically. The signs include cell nuclear irregularity, increased mitotic activity, and abnormalities of differentiation, often combined with inflammatory infiltrates, and stromal changes. The risk of such precancerous lesions becoming malignant can be established only in the light of experience of their behaviour in each particular site in which they occur.
- Some benign tumors . Probably al benign tumors carry some risk of malignancy, but in most cases it is little more than that of normal tissues, while in other is considerably high. There is little obvious logic about the differences. The villous papilloma of the rectum becomes malignant more often than the adenomatous tubular polyp of the same site; similar tumors of the stomach carry a worse prognosis that other gastrointestinal segment tumors, while the uncommon similar tumors of the small intestine only very rarely become invasive (malignant). Comparable anomalies could be quoted at other sites.
- Certain chronic diseases. Carcinoma (cancer) may develop as a more or less common complication of some noncancerous diseases, such as cirrhosis of the liver, ulcerative colitis, asbestosis, and a variety of skin diseases.
- Cancer in situ. Most cancers begin as localized growths confined to the epithelium in which they arise. As long as these early cancers do not penetrate the basement membrane on which the epithelium rests, such tumors are termed cancer in situ.
In some tissues, particularly the epidermis of the skin, the squamous epithelium of the exocervix, endometrium, and the bronchial epithelium, an area of atypical proliferation of cells occurs, affecting usually the entire thickness of the epithelium and exhibiting the cytological features similar to those of invasive cancer, but no demonstrable penetration into the subephitelial stroma was discovered. It is generally believed that this lesion, cancer in situ, is a true intraepithelial cancer that frequently becomes invasive cancer if left untreated. The lesion is also known as preinvasive carcinoma.
In this stage, it is unfortunate that carcinomas are asymptomatic, because they are invariably curable. When the in situ cancer acquires invasive potential and extends directly through the underlying basement membrane, it is in a position to compromise neighbouring tissues and to metastasize. In those situations in which cancer arises from cells that are not confined by a basemnet membrane, such as connective tissues cells, lymphoid nodes, and hepatocytes, the in situ cancer stage is not defined.
The degree of risk of developing cancer varies greatly with different lesions, and is often hard to determine with any exactness. In a few rare conditions, such as polyposis coli, and xeroderma pigmentosa, it is practically 100%. In cancer in situ of the cervix, extesively studied but still controversial, it may also be high though, a period of 20 years may elapse between the appearance of the lesion and the onset of invasive cancer. In most lesions the risk appears to be much lower.