DMBA-induced rat skin tumours were studied using molecular markers immunohistochemistry to elucidate different stages of chemical carcinogenesis and their evaluation in diagnosis of neoplasms in animals. Skin cancer produced through sequential histopathological changes: epidermal hyperplasia/hyperkeratinization, severe epidermal hyperplasia, papilloma, papillary carcinoma, squamous cell carcinoma/its metastasis in lungs and adnexal neoplasms. Among indices for proliferation markers (mitoses, AgNORs and PCNA), PCNA index was most reliable to differentiate benign papillomas with borderline...