Table 7.

Criteria of malignancy in mammary tumors

I. Macroscopic criteria

Rapid growth and skin ulceration in short period of time Soft, fleshy appearance with or without areas of necrosis and hemorrhage

II. Histopathologic criteria

Loss of normal architecture with varying pleomorphism and layering or formation of papillae One cell type, basically intermediate cells, predominate over the dark or myoepithelial cells. Varying response of the host such as fibrosis or inflammatory response. Increased nucleocytoplasmic ratio, round to oval nuclei with smooth contour, leptochromatic appearance, and 1 or 2 prominent nucleoli, numerous mitoses Invasiveness: neoplastic cells infiltrating surrounding structures such as muscle, dermis, and fat

III. Biologic criteria

Metastases to lymph nodes and lungs, occasionally found in older animals, rarely found in young animals Transplantability, although it may not be a reliable criterion because benign fibroadenoma may be also transplantable Angiogenic response in anterior chamber of the eye, found in malignant and premalignant lesions