Cancer begins to originate, when cell breaks out from the control of mechani­sms deciding of its divisions and localisation" – this is an opinion of Robert A. Weinberg, Laboratory of Researches on cancer director in Whitehead Institute of Technolo­gy, and the most accurately gives matter of neoplastic process. Healthy cells maintain balance between dividing and differentiation and decay. Neoplastic cells, thanks to differentiation and ability to uncontrollable growth, become immortal. They are also able to migration and invasion of regions up to now occupied by other types of cells. This is why they are such a big danger for the whole organism.

Transformation of normal into neoplastic cells is called the neoplastic transformation. Genes, which activation may lead to transfor­mation, are called protooncogenes. They are located in genetic material of each healthy cell and code proteins, taking part in regulation of divisions. Excessively active protooncogenes are called oncogenes and can be found in neoplastic cells. Result of their action can be compared to location of brick on accelerator pedal in car. Also other possibility of improper acceleration of divisions exists. This is a “damage of breaks", that is mutation in suppressor genes (antioncogenes).

Stages of neoplastic transformation

The first stage of neoplastic transformation is called preinitiation. In this period cell is exposed to action of carcinogenic factors. Ionizing radiation (Roentge­n's, radiating isotopes’, i.e. radium or uranium), causing the most frequently tumours of bone marrow and lymphatic system, are the most dangerous factors. Also ultraviolet radiation (sun or quartz lamp in solarium), which causes skin tumours, is dangerous. Very many carcinogenic substances are present in cigarettes smoke. They cause not only malignant tumours of lung, but also of lower lip, oral cavity, larynx, esophagus, urinary bladder, kidney, pancreas and cervix. It is estimated, that smoking is a main cause of about 20% of all deaths on the world on neoplastic disease. Tumour may also develop as a result of viral infection, presence of bacterial and parasitic toxins and hormonal disturbances, for example excessive amount of estrogens.

In preinitiation stage genetic predispositions play very important role. They are connected with changes in genes, which products participate in removal of carcinogenic factors from the organism and in repair of developing destructions. However the tumour may develop as effect number of mutations also in these people, who lead healthy life style and are no burdened with genetic propensities.

The next stage of neoplastic transformation is initiation. It begins together with appearance of the first mutation. If attacked cell possesses ability to divide, evoked mutation is consolidated and passed over to the next generations. Such mutated cell is called in other words initiated.

The third phase of transformation is promotion. Initiated cell undergoes many further mutations, and become a typical neoplastic cell. One of the most important features differentiating normal from initiated cells is fact, that the last ones are characteristic for disturbed abilities of adhesion to surrounding cells. This feature in early period of tumour development enables them crossing of natural barriers between tissues, and in the next period may enable migration and metastases formation. In this phase stopping the process of the tumour formation by organism is still possible, what is observed in majority of people.

The last phase of transformation is progression. Then growth of neoplastic cells, which usually has uncontrolled course and is irrevocable, is observed. Just in this period the first symptoms of disease enabling its clinical diagnosis appear.

The critical moment in the tumour’s development is establishment of such size, in which too small amount of supplemented oxygen, nutritional substances and growth factors begin to limit its growth. Then some state of balance is established, which may last for many years. Further growth of tumour is possible soon after the increase of food and oxygen supplementation. The only method to obtain this aim is tumour’s vascularization. The process of vessels formation (angiogenesis) is constantly controlled by the balance of pro- and antiangiogenic factors. In adult process of angiogenesis is observed only during healing of wounds and in this case only is profitable for organism. In neoplastic cells uncontrolled proliferation of vessels is observed. Better nourished tumour’s cells rapidly start to divide and their growth additionally stimulates secretion by developing vessels more and more amounts of stimulating factors. Stimulation of functions of these genes, which products enable the tumour’s cells fast growth and formation of invasive infiltrations, is also observed. The critical moment in transformation of preinvasive into infiltrating cancer is destruction of basement membrane that is penetration of neoplastic cells to deeper layers of tissues. The bigger the neoplastic focus is the bigger infiltration and frequency of metastases. Infiltration of the tumour is conditioned by production of pathological tissue the enzymes able to destroy intracellular substance.

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