Paradoxes in carcinogenesis: new opportunities for research directions.
BACKGROUND
The prevailing paradigm in cancer research is the somatic mutation theory that posits that cancer begins with a single mutation in a somatic cell followed by successive mutations. Much cancer research involves refining the somatic mutation theory with an ever increasing catalog of genetic changes. The problem is that such research may miss paradoxical aspects of carcinogenesis for which there is no likely explanation under the somatic mutation theory. These paradoxical aspects offer opportunities for new research directions that should not be ignored.


CONCLUSIONS
Various paradoxes related to the somatic mutation theory of carcinogenesis are discussed: (1) the presence of large numbers of spatially distinct precancerous lesions at the onset of promotion, (2) the large number of genetic instabilities found in hyperplastic polyps not considered cancer, (3) spontaneous regression, (4) higher incidence of cancer in patients with xeroderma pigmentosa but not in patients with other comparable defects in DNA repair, (5) lower incidence of many cancers except leukemia and testicular cancer in patients with Down's syndrome, (6) cancer developing after normal tissue is transplanted to other parts of the body or next to stroma previously exposed to carcinogens, (7) the lack of tumors when epithelial cells exposed to a carcinogen were transplanted next to normal stroma, (8) the development of cancers when Millipore filters of various pore sizes were was inserted under the skin of rats, but only if the holes were sufficiently small. For the latter paradox, a microarray experiment is proposed to try to better understand the phenomena.


CONCLUSIONS
The famous physicist Niels Bohr said "How wonderful that we have met with a paradox. Now we have some hope of making progress." The same viewpoint should apply to cancer research. It is easy to ignore this piece of wisdom about the means to advance knowledge, but we do so at our peril.
Baker
Stuart G
SG
Division of Cancer Prevention, National Cancer Institute, Bethesda, MD, USA. sb16i@nih.gov
Kramer
Barnett S
BS
D000818:Animals; D002273:Carcinogens / Q000494:pharmacology; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D004247:DNA; D004260:DNA Repair; D006801:Humans; D009154:Mutation; D009365:Neoplasm Regression, Spontaneous; D009369:Neoplasms / Q000209:etiology* / Q000235:genetics / Q000473:pathology; D051381:Rats; D012106:Research / Q000639:trends*
D002273:Carcinogens; D004247:DNA