Carcinogenesis, retinoid effects

Retinoids in Cancer Prevention and Treatment Since the discovery of vitamin A, the observation that the main effects of deficiency are hyperplasia and loss of differentiation of squamous epithelium has raised speculation that the vitamin may he associated with carcinogenesis. Either deficiency may be a risk factor for cancer or increased intake may be protective. Deficient animals develop more spontaneous tumors and are more sensitive to chemical carcinogens, whereas liver reserves of vitamin A are lower in patients with cancer than in controls. One of the genes repressed by retinoic acid is the myc-oncogene. 

In addition to the regression of established tumors, a number of retinoids show apparent inhibition of the chemical induction of the bladder and other epithelial tumors in experimental animals. The effect is not in fact inhibition of carcinogenesis, but rather a lengthening of the latent period between the initiation step of carcinogenesis and the development of mmors. Although perhaps not as exciting as compounds that prevent the development of cancers, such a delaying action may be usefitl. If the results can be scaled from... 

As detrimental effects result from deficiency as well as an excess of retinoids and carotenoids, and since both have similar adverse effects in terms of fibrosis, carcinogenesis, and possibly embryotoxicity, therapeutic measures must pay attention to the narrow therapeutic window, especially in drinkers, in whom alcohol narrows the therapeutic window even further by promoting the depletion of retinoids and by potentiating their toxicity (91). 

Zheng Y, Cramer PM, Lubet RA, Steele VE, Kelloff GJ, Pereira MA (1999) Effect of retinoids on AOM-induced colon cancer in rats modulation of cell proliferation, apoptosis and aberrant crypt foci. Carcinogenesis 20 255-260... 

Effects of Retinoids on Chemically Induced Carcinogenesis and Photocarcinogenesis... 

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