REPORT OF A CASE
A 77-year-old white woman presented with multiple (>50) erythematous, keratotic papules and plaques distributed diffusely on her trunk and extremities, including the sole of her left foot. These lesions varied in size from 2 mm to 6 cm in diameter (Figure). The patient noted an increasing number of lesions at a rate of approximately 2 to 3 new plaques per month. An excisional biopsy specimen of the largest and most irregular lesion on her back demonstrated invasive squamous cell carcinoma (SCC). Three more biopsies were performed, specimens of which showed full-thickness epidermal cell atypia and disorder consistent with Bowen disease (SCC in situ). The patient had 1 slightly pearly nodule on her neck that was clinically and histologically consistent with basal cell carcinoma.The patient grew up in rural Montana and had been exposed to arsenic in the well water and had also been given an