Number of nucleoli and nucleolar organizer regions per nucleus and nucleolus - Prognostic value in canine mammary tumors

Twenty-eight canine mammary tumors were evaluated for histopathologic classification as recommended by the World Health Organization and silver-binding nucleolar organizer region (AgNOR) and nucleolus counts. Samples of surgically excised tumors and tumors taken at necropsy were fixed in neutral formalin, embedded in paraffin, and cut into 1-3-mu m-thick sections. Two sections were taken from each tumor: one was stained with hematoxylin and eosin and the other was treated with the silver staining technique for the demonstration of AgNORs. After histopathologic classification, the number of nucleoli and the number of AgNORs/nucleus and AgNORs/nucleolus were determined. Statistical analysis (Student's t-test) showed a significant difference in the mean number of nucleoli (P < 0.005), mean number of AgNORs/nucleolus (P < 0.001), and mean number of AgNORs/nucleus (P < 0.005) between benign and malignant canine mammary tumors. There was no significant differences between metastatic and nonmetastatic malignant tumors.