Histopathologic characterization of mammary neoplastic lesions induced with 7,12 dimethylbenz(alpha)anthracene in the rat: a comparative analysis with human breast tumors.

CONTEXT: The dimethylbenz(alpha)anthracene (DMBA) breast cancer model induced in the rat is used for the study of mammary carcinogenesis because it closely mimics human breast disease.
OBJECTIVE: To analyze the histopathologic features of mammary carcinomas induced in the DMBA experimental model, in a manner similar to that used in human pathology, to allow a comparative analysis between both systems.
DESIGN: Three experimental series of 20 animals were used. At 53 days of age, a single dose of 5 mg of DMBA per rat was given. Mammary tumors were collected when the rats were killed. Several histopathologic parameters were studied. For grading, the parameters described in the modified Scarff-Bloom-Richardson scheme were used, adapted to rat mammary tumors.
RESULTS: More than 50% of the carcinomas presented a pattern grade I, a nuclear grade I or II, and fewer than 10 mitoses/10 high-power fields (P <.05). Although the tumors were generally well differentiated, they showed a range of differentiation. More than 85% of carcinomas did not display tumoral necrosis (P <.05). This feature was observed mostly in high-grade carcinomas. There was no or scanty lymphoplasmacytic infiltration in more than 70% of carcinomas (P <.05). The degree of infiltration increased with the histologic grade. Microcalcifications were found rarely (P <.05). The carcinomas exhibited a mixed structural pattern, most with a predominant cribriform pattern (P <.05). No or light (+) stromal response was seen in most cases (P <.05). Some carcinomas, especially when poorly differentiated, presented a desmoplastic reaction. Most carcinomas presented scanty mast cell infiltration (P <.05), no features of secretion (P <.05), and absence of microcribriform pattern (P <.05). These features were seen more often in low-grade carcinomas.
CONCLUSIONS: Despite the presence of some structural differences, rat mammary adenocarcinomas and the most common human breast carcinomas share several morphologic similarities. Moreover, some features could be related to the aggressive behavior of the tumor. The analysis carried out in this study, similar to that done in human pathology, allows a more extensive understanding of mammary tumors in rats, as well as a more accurate use of this animal model, and has made it possible to develop an innovative classification of rat mammary lesions.