Table 1.

Histological staging system proposed for canine mammary carcinomas.

Stage	Invasiveness	Pathologic tumor size	Lymphovascular invasion	Pathologic nodal stage
Stage 0	In situ	Any pT	LVI–	pN0 or pNX
Stage I	Invasive	pT1 ≤ 20 mm	LVI–	pN0 or pNX
Stage II		pT2 > 20 mm
Stage IIIA		pT1 ≤ 20 mm	LVI+ and/or pN+
Stage IIIB		pT2 > 20 mm

LVI–, absence of lymphovascular invasion.

LVI+, presence of lymphovascular invasion.

pN0, absence of nodal metastasis.

pN+, presence of nodal metastasis.

pNX, nodal stage unknown.