To the Editor.—
There has been concern that isoniazid (INH) may be carcinogenic for man1,2 since it contains hydrazine, a known carcinogen,3 and because it produces a variety of experimental tumors (IARC Monogr Eval Carcinog Risk Chem Man 4:159, 1974). We report two cases of bile duct cancer where there was exposure to INH.
Report of Cases.—
A 55-year-old man had a well-differentiated bile duct cancer at the junction of the right and left hepatic ducts 18 years after receiving INH (total dose, 122 g) for pulmonary tuberculosis. A 71-year-old alcoholic man was hospitalized with obstructive jaundice two years after receiving INH (total dose, 36 g) for suspected tuberculosis. He also had a well-differentiated bile duct adenocarcinoma.Although the relation between INH exposure and these two rare cancers may only be coincidental, these were the only bile duct cancers encountered at our hospital from 1970 to 1977, a