Carcinogenic risk, influencing

The National Coimdl on Radiation Protection and Measurements (NCRP) has been concerned from its inception with assessment of the risks of low-level irradiation. In recent years, this concern has prompted increasingly detailed efforts to quantify the influence of dose, dose rate, and linear energy transfer (LET) on the biomedical effects of radiation, with particular reference to the carcinogenic risks of low-level exposure (NCRP, 1980) and the work-in-progress of NCRP Sdentific Committee 40 on LET and relative biological effectiveness. 

Tretinoin or retinoic acid is the acid form of vitamin A. Actually it is the all-trans isomer of retinoic acid. It is an effective topical agent for acne vulgaris. Its mechanism of action is believed to be associated with increased epidermal cell turnover. Some 10% of the topically applied dose is absorbed, metabolized by the liver and excreted in the urine and bile. To be effective tretinoin should be applied in a concentration that results in mild irritation and erythema. Patients should be advised to avoid or minimize sun exposure and use a protective sun screen as animal studies have raised some concern about possible carcinogenic effects under the influence of ultraviolet radiation. There are no indications that topical tretinoin is associated with an increased risk for birth defects. 

For better or worse, the approaches to risk assessment that have been developed for purposes of radiological protection have set a pattern which has influence approaches for assessing the risks of chemical mutagens and carcinogens. 

Current concerns with estrogenic compounds and their influence on a broad range of reproductive disorders, along with possible carcinogenic effects, have renewed interest in chlorinated pesticides. The need for ongoing scientific research to assess the potential risk posed by these compounds seems inevitable. 

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