Cancer biology

Cancer is a proliferation of cells which grow in an uncontrolled manner, invading local tissues and spreading widely through the blood or lym-phatics to produce secondary deposits, or metastases in distant parts of the body.

The word 'cancer' comes from Latin, meaning a crab. A tumour was called a cancer because of swollen veins around the area resembling a crab's limbs. The study of cancer is called Oncology. Oncology is a word derived from the Greek, onchos, a lump, or tumour. The abnormal tissue growth is called neoplasm. If a neoplasm can cause harm by spreading, it is said to be malignant.

Cancer was known to ancient civilizations. However the disease as it would be defined today was established as an entity by German pathologists of 19th century. They described cellular nature of cancer and classified cancer. At the beginning of the 20th century, most major forms of cancer had been described. Further, attention was focused on finding the cause and intro-ducing treatment. In 1775 Pott recognised cancer in chimney sweeps. He associated soot with cancer. From this time onwards environmental and oc-cupational hazards were recognised as follows :

shale oil                           skin cancer in workers

radio active ores             lung cancer in miners

beta-naphthylamine        bladder cancer in rubber industry workers

cigarettes                        lung cancer

Later it was discovered that certain viruses can also cause cancer. One of the earliest virus, causing cancer, described was Rous sarcoma virus. Recently, human T-cell leukaemia has been found to be due to the virus HTLV-1.

Some forms of cancer can also be inherited. A rare eye tumour, retinoblastoma is inherited. It is a dominant character showing Mendelian in-heritance.

Cancer biology

The knowledge of cancer biology is growing rapidly. Researches are being conducted to fully understand the development of cancer at the cellular

or molecular level. The available information is not sufficient for satisfactory treatment of cancer.

During normal development and growth the cells in our body divide mitotically and get differentiated to specialized cells of the tissues. The pro-cesses of cell mitosis, growth and differentiation are controlled by cellular genes. Cancer is caused due to mutation or abnormal activation of such genes. such a mutation can happen in a single cell. Thus it may be monoclonal in origin. With further growth of cancer, additional mutations may occur in the daughter cells giving rise to subclones. The mutated cells may remain as heterogeneous cancer cells. Among these subclones some may have greater capacity and metastasize to distant tissues. They may also remain more resistant to damage from various anticancer treatments.

The cancer cells have characteristic properties. They can be differ-entiated from normal cells under microscopic observation. These cells have large nuclei. In each cancer cell, the ratio of nucleus to cytoplasm is high. They have prominent nucleoli. The cells can grow indefinitely in culture me-dium. As component cell of a tissue they remain less differentiated. Even after getting organised into tissues unlike other cells they do not lose their replicative capacity. Cancer cells have the ability to invade surrounding tissues.

The sequence of events that convert a normal cell into a cancer cell is called carcinogenesis. The process of carcinogenesis includes, intiation, growth, promotion, conversion, propagation and progression. Progression includes the processes of invasion and metastasis.

Mature cancers have relatively uncontrolled growth, behaviour. As other normal cells they do not show any of the normal intracellular and extracellular growth control mechanisms. Initially the cancer cells have an exponential growth. Gradually their growth surpasses blood vascular supply. This results in slowing down of growth.