SMO and cancer: Squamous cell carcinomas account for more than 90% of oral malignant tumors and often begin with precancerous lesions.197 Shh expressed in oral epithelial dysplasia and carcinoma in situ.198 Also, Shh, Gli2, Smo, and Ptch are highly expressed in precancerous lesions of oral mucosa.199 Higher expression levels of Ptch1, Smo, and Gli1 were found in oral squamous cell carcinoma (OSCC) cases when compared to nonneoplastic oral mucosa.