Cancer cells are defined by two heritable properties: they and their progeny (i) reproduce in defiance of the normal restraints on cell division and (2) invade and colonize territories normally reserved for other cells.
The controlling mechanism in the cell proliferation is maintained by a chain of events. Very occasionally, this control breaks down. A cell then begins to grow and divide in an unregulated fashion without regarding the body’s need. The descendant cells also proliferate without responding the regulation, as a result a clone of cells will be able to expand indefinitely, and will give rise to a tumor or neoplasm.
Normally, the neoplastic cells remain clustered together in a single mass, which is called a benign tumor. By removing the mass of tissue surgically one can achieve a complete cure from the tumor. A tumor can be transformed into a cancer, if it is malignant, i.e., if cells acquire an ability to invade the surrounding tissue and then through circulation these loose cells form there a secondary tumor. The process of spreading of cancer cells through circulation and invading into a new location is called metastasis.
Cancer may be classified according to the cell or tissue types. The cancer arising from epithelial cells is termed as carcinoma, those arising from connective tissues or muscle cells are termed as sarcomas.
At present, the set of names for malignant tumors and benign tumors have been given. For example, a benign epithelial tumor with glandular organization is known as adenoma; the same type of tumor with malignant from is known as adenocarcinoma. Similarly chondroma and chondrosarcoma are termed for benign and malignant tumors of cartilages respectively.
The basal carcinoma is derived from the keratinocyte stem cell of the skin and which will generally continue to synthesize cytokeratin intermediate filaments, this is only locally invasive and rarely metastatic. Melanoma is derived from pigment cells of the skin, continue to make pigment granules, if not removed properly, is much more malignant and rapidly gives rise to many metastases.
Distinction between normal cell and cancer cell
Cancer cells can be distinguished from normal cells by microscopic examination. Cancer cells are usually less well differentiated, with a high nucleo-cytoplasmic ratio, prominent nucleoli, many mitoses and relatively little specialized structure.
Cancer cells are characterized by an unc0ntrolled cell growth, invasion of other tissues and dessemination to other sites of the organism producing secondary carcinogenesis. All of these characteristics suggest that cancer cells have escaped from the controls that regulate normal growth.
The cancerous tumors are monoclonal, i.e., most cancers derive from a single abnormal cell which undergoes some heritable changes that enable it to outgrow others.
Although, malignant cells retain resemblance morphologically to some extent to the normal cell type from which they arose but they are certainly different from cytological, molecular, and general point of view.