the present invention is directed to methods and compositions of treating or preventing epithelial lining tissue damage from dermatitis or mucositis induced by radiation exposure and / or chemotherapy , by applying to skin , mucosa or other tissues of the body an amount of a therapeutic composition which comprises a histone deacetylase inhibitor formulated with at least one pharmaceutically acceptable biocompatible polymer or carrier , or pharmaceutically acceptable salts in an amount sufficient to delay onset or decrease severity of the signs and symptoms of dermatitis and mucositis in cancer therapy . such therapeutic compositions have the advantage of prolonged retention and sustained action of the histone deacetylase inhibitor in the skin , mucosa or other tissues of the body . the invention is also directed to treatment and prevention of gastrointestinal distress and cancer - related fatigue syndrome that are associated with mucositis in cancer therapy .