Table 1.

Histologic features of the different categories of columnar cell lesions in canine mammary gland.

Columnar Cell Change without atypia (CCC)	Columnar Cell Hyperplasia (CCH)	Flat Epithelial Atypia (FEA)	Flat Epithelial Atypia (FEA)
		CCC with atypia	CCH with atypia
One to two columnar cell layers with uniform ovoid to elongated nuclei; nucleoli absent or inconspicuous.	Cellular stratification more than two columnar cell layers with uniform ovoid to elongated nuclei; nucleoli absent or inconspicuous.	One to two columnar cell layers with complex architectural patterns present; Mild to moderate cytologic atypia present (usually low-grade): round-to- ovoid, mildly pleomorphic and hyperchromatic nuclei, with inconspicuous nucleoli.	Cellular stratification more than two columnar cell layers with complex architectural patterns present; Mild to moderate cytologic atypia present (usually low-grade): round-to- ovoid, mildly pleomorphic and hyperchromatic nuclei, with inconspicuous nucleoli.

Classification categories are based on an expanded version of those describes by Schitt and Vincent- Salomon [5].