A 60-year-old man who worked for 30 years in a chemical factory complains of blood in his urine. Urine cytology discloses dysplastic cells. A bladder biopsy demonstrates transitional cell carcinoma. Which of the following carcinogens was most likely involved in the pathogenesis of bladder cancer in this patient?

Transitional cell carcinoma is the most common malignant tumor of the urinary bladder, and the incidence of bladder cancer is increased in aniline dye workers. These azo dyes are converted to water-soluble carcinogens in the liver. They are excreted in the urine, where they primarily affect the transitional epithelium of the bladder. Benzene exposure (choice C) is associated with leukemia. Vinyl chloride exposure (choice E) has been associated with hepatic angiosarcomas.Diagnosis: Transitional cell carcinoma of bladder