Solid Carcinoma of the Canine Mammary Gland: a Histological Type or Tumour Cell Arrangement?

Mammary neoplasms are the most frequently diagnosed tumours in female dogs and are classified into various histological types, including solid carcinomas. We proposed a subclassification of solid carcinomas based on morphological and immunohistochemical characteristics, and correlated the subtypes with prognostic factors. A total of 135 cases of solid mammary carcinoma were selected from 3,400 canine mammary neoplasms in the archives of the Laboratory of Comparative Pathology, Institute of Biological Sciences, Federal University of Minas Gerais, Brazil. Epidemiological and survival data were obtained, and immunolabelling for chromogranin A, pancytokeratin, cytokeratin 14, Ki67 and p63 was performed. Solid carcinomas were classified into six subgroups: malignant adenomyoepithelioma (68/135), carcinoma with solid pattern (22/135), malignant myoepithelioma (16/135), basaloid carcinoma (14/135), neuroendocrine carcinoma (10/135) and solid papillary carcinoma (5/135). Shorter survival time was associated with the presence of lymphatic invasion (P = 0.009) in the initial clinical staging (I-III). When considering all clinical stages (I-V), vascular invasion (P <0.001) and the presence of regional metastasis (P = 0.004) were important prognostic factors. Basaloid carcinoma and solid papillary carcinoma did not reach the median survival time for early-stage cases, and malignant myoepithelioma had the highest median survival in advanced stages. Carcinoma with a solid pattern was associated with a higher number of regional metastases. Distinguishing the various histological and immunophenotypic subtypes that exhibit a solid arrangement, using histological and immunohistochemical criteria, is essential for understanding the behaviour of these neoplasms and for the selection of more appropriate and specific therapies.

C(3)1-TAg in C57BL/6 J background as a model to study mammary tumor development.

Diagnosis and prognosis of breast cancer is based on disease staging identified through histopathological and molecular biology techniques. Animal models are used to gain mechanistic insights into the development of breast cancer. C(3)1-TAg is a genetically engineered mouse model that develops mammary cancer. However, carcinogenesis caused by this transgene was characterized in the Friend Virus B (FVB) background. As most genetic studies are done in mice with C57BL/6 J background, we aimed to define the histological alterations in C3(1)-TAg C57BL/6 J animals. Our results showed that C3(1)-TAg animals with C57BL/6 J background develop solid-basaloid adenoid cystic carcinomas with increased fibrosis, decreased area of adipocytes, and a high proliferative index, which are triple-negative for progesterone, estrogen, and human epidermal growth factor receptor 2 (HER2) receptors. Our results also revealed that tumor development is slower in the C57BL/6 J background when compared with the FVB strain, providing a better model to study the different stages in breast cancer progression.