The document discusses precancerous dermatoses including arsenical keratoses and carcinoma in situ. It defines arsenical keratoses as lesions that develop after prolonged ingestion of arsenic at doses above 50μg/L for over 6 months. It occurs commonly in areas with high environmental or occupational arsenic exposure like parts of India, Taiwan, and Bangladesh. Prolonged arsenic exposure can cause multiple abnormalities like chromosomal damage and oxidative stress leading to increased risk of progression to squamous cell carcinoma. Carcinoma in situ is described as an intraepidermal form of squamous cell carcinoma that appears as well defined erythematous scaly or crusted plaques, most commonly affecting older