- The subject has used topical or systemic therapies that might interfere with the evaluation of the study medication during the study; specifically these include the topical use to the study tumors of: glucocorticoids (ii) retinoids (e.g., etretinate, isotretinoin, tazarotene, tretinoin, adapalene) systemically or topically (iii) alpha-hydroxy acids (e.g., glycolic acid, lactic acid) to more than 5% of the skin during the six months prior to study entry (iv) 5-fluorouracil or imiquimod; also - treatment with systemic chemotherapy or agents known to be inhibitors of HH signaling within 60 days to starting study medication