Global protein analyses of canine mammary gland tumors

Because reliable diagnostic markers for an early differentiation of non-metastasizing from metastasizing carcinomas are lacking, a prediction of the metastatic potential of canine mammary tumors is still impossible before metastasis actually occurs. Furthermore, it is still unclear whether metastatic behavior is an inherent feature or a result of a time dependent linear malignant progression. Therefore, the present study visualized and compared the protein expression patterns of canine normal mammary gland, adenomas, non-metastasizing and metastasizing carcinomas by 2D-DIGE and identified subsequently differentially expressed proteins by mass spectrometry. Differentiation of non-metastasizing and metastasizing carcinomas was based on the lymph node status at the time of surgical excision of the primary tumor mass. The following hypotheses were tested here: 1. The metastatic potential of canine mammary tumors is reflected in their protein expression patterns and these differentially expressed proteins are potential metastasis markers. 2. Carcinogenesis of canine mammary tumors is associated with malignant progression from normal mammary gland towards metastasizing carcinomas. On the molecular level, this malignant progression is associated with a continuous and linear change of quantitative protein expression levels over the subsequent stages of malignancy.