Bioassay of Selenium Sulfide (Gavage) for Possible Carcinogenicity (CAS No. 7446-34-6)

Selenium sulfide is an ingredient in dandruff shampoos used in concentrations of 1% in products sold over-the-counter and 2.5% in products which are available by prescription only. Prescription shampoos have been shown in clinical studies to be of therapeutic value against dandruff. An antimitotic mechanism of action is suggested by data showing that selenium sulfide decreases the rate of incorporation of radioactively labeled thymidine into the DNA of dermal epithelial cells. Approximately 200 kg of selenium sulfide is estimated to be used annually for this purpose. A bioassay of selenium sulfide for possible carcinogenicity was conducted by administering this substance by gavage to F344 rats and B6C3F1 mice. Groups of 50 rats and 50 mice of each sex were administered selenium sulfide suspended in 0.5% aqueous carboxymethylcellulose 7 days per week for 103 weeks at either 3 or 5 mg/kg/day for rats and 20 or 100 mg/kg/day for mice. As vehicle controls, groups of 50 rats and 50 mice of each sex were administered only the 0.5% aqueous carboxymethylcellulose. Similar groups of untreated controls also were used. All surviving rats and mice were killed and necropsied at week 104 or 105. The significant effects that could be related to administration of selenium sulfide at the doses used were decreased body weight and increased tumor formation in female mice and in rats of each sex. Dosed rats and female mice had an increased incidence of hepatocellular carcinomas and adenomas. Dosed female mice also had an increased incidence of alveolar/bronchiolar carcinomas and adenomas. Under the conditions of this bioassay, selenium sulfide was carcinogenic for F344 rats and female B6C3F1 mice, including hepatocellular carcinomas in male and female rats and female mice and alveolar/bronchiolar carcinomas and adenomas in female mice. Selenium sulfide was not carcinogenic for male mice; but they have been able to tolerate higher doses. Levels of Evidence of Carcinogenicity: Male Rats: Positive Female Rats: Positive Male Mice: Negative Female Mice: Positive