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Abstract:
Cell proliferation in the organism is accompanied by cell displacement. Proliferating tissues exhibit three key characteristics: a site of origin of the stem cell, a tissue radius along which all constituents except the stem cell are displaced and a periphery where cells are eliminated. The tissue thus consists of two cell types: Stem and transitional. Since only the first resides permanently in the tissue any lasting change observed in the tissue is directed by the stem cell. Each stem cell division results in two cell types: one replacing the parent cell to remain a stem cell, while the other originates an outward displaced transitional cell clone whose life span is limited. In the normal state, the stem cell pool is constant, although its replenishment capacity is limited. Neoplasia is regarded here as a purposeful tissue alteration originating in a stem cell change manifested by: Aneuploidy, maturation arrest, stem cell pool enlargement and increasing cell turnover. Stem cells are assumed to secrete a substance 'A' necessary for a proper tissue function, whose production is impeded by carcinogens, mainly by stem cell depletion. Since however stem cell replenishment is limited, the organism grows a specialized organ, the neoplasm, producing a less efficient substitute for 'A', denominated here as substance 'B'. Neoplastic growth is indirectly dependent upon the abundance of substance 'A', the supply of which should be followed by a reduction of neoplastic mass. Neoplasia is thus viewed here as a protective function directed by the stem cell and linked with "oncogenes". Each determined stem cell is harbouring a specific oncogene and exhibits a typical neoplasm. Since the theory predicts that neoplastic growth indirectly depends upon the abundance of substance 'A', it may be tested by investigating the effect of substance 'A' producing stem cells upon the growing neoplasm. Their supply to the organism should be followed by a reduction of the neoplastic mass.