Expression of the oncogene c-erbB-2 in canine mammary cancers and tumor-derived cell lines

To determine, for canine mammary tumors, whether malignancy, with or without local invasion or regional metastasis, was associated with overexpression of the oncogene c-erbB-2.

c-erbB-2 expression was measured in canine mammary tumor-derived cell lines and in mammary tumor tissues from clinical cases. Clinical samples were examined histologically to determine whether they were benign or malignant and, if malignant, whether they had evidence of local invasion or regional metastasis. Canine fibroblast cultures and normal canine mammary epithelial tissues were used as reference standards for cell lines and mammary tumors, respectively. SAMPLE POPULATIONS: 28 canine mammary tumor tissue samples obtained surgically from clinical cases and samples from 7 canine mammary tumor cell lines derived from primary canine mammary tumors.

c-erbB-2 mRNA levels were determined by means of hybridization of total polysomal RNA with a 32P-labeled human c-erbB-2 probe on dot blots, and results were quantified by means of scanning densitometry. Overexpression of c-erbB-2 was defined as an autoradiographic density > or = 2 times the density of reference samples on the same blot.

Overexpression of c-erbB-2 was detected in 17 of 23 malignant tumors, 0 of 5 benign tumors, and 2 of 7 mammary tumor cell lines. c-erbB-2 overexpression was correlated with a histopathologic diagnosis of malignancy (P = 0.005) but not with the presence of local invasion or regional metastatic disease (P = 0.621).

Results suggest that overexpression of c-erbB-2 occurs prior to the development of metastatic disease in canine mammary tumors and plays a role in the development of malignancy.