Abstract
It is well documented that despite global abnormalities of the immune system in AIDS and other immune deficiency diseases or in immunosuppressed patients the incidence of only a few kinds of tumour increases and even in the development of tumours in question the degree of immunosuppression seems not to be a critical factor. It results from this that the known immune system has no significant role in the mechanism that prevents the development of tumours. Consequently, the fact that tumours do not develop in the majority of the population during their lifetime, indicates the existence of other defence systems. We assumed that the defence is made by small substances of the circulatory system. Substantial evidence exists that the uptake of the majority of these substances is increased and unregulated by tumour cells and proportional to their availability. This feature of tumour cells maybe fatal when the number of cells is still low and there are abundant substances in their environment because some substances may be toxic if their concentrations can reach high level in the cells. Thus, the arising cancer cells die in the majority of the population during their lifetime if the number of cells arisen is not too high, or the concentrations of the required substances are not too low. To our hypothesis, the above effects of the physiological mixture of the given molecules in the blood form the Passive Antitumor Defence System (PADS). This hypothesis is confirmed by our experiments and supported by epidemiological, clinical observations and other literary data.
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