Histopathological Analysis of Invasive Bladder Carcinomas Induced by 3,2′‐Dimethyl‐4‐aminobiphenyl in Hamsters

Histopathological characteristics of urinary bladder tumors induced in Syrian golden hamsters by 3,2′‐dimethyl‐4‐aminobiphenyl (DMAB) were analyzed. DMAB was subcutaneously injected in corn oil at a concentration of 100 mg/kg once a week for 20 weeks and ethinyl estradiol (EE) was administered in the diet at a dose of 0.75 ppm throughout the experiment. A small group of animals was killed at week 20 and all survivors were killed at week 50. Urinary bladder carcinomas were induced in 14 of 18 hamsters (78%; 0.89/animal) in the DMAB+EE group and 11 of 17 (65%; 0.88/animal) in the DMAB alone group in males, and in 11 of 14 (79%; 0.79/animal) in the DMAB+EE group and 4 of 5 (80%; 0.80/animal) in the DMAB alone group in females examined between weeks 20 and 50. All were non‐papillary invasive transitional cell carcinomas partly demonstrating glandular and/or squamous differentiation, and most carcinomas developed in the bladder neck. Degree of invasion was clearly correlated with degree of morphological atypism in the transitional cell carcinomas, hut not with squamous or glandular differentiation. No sex difference or modifying effect of EE on DMAB urinary bladder carcinogenesis was evident. No bladder carcinomas were observed in non‐DMAB‐treated animals.