Collagen fibers in grades I, II, and III of the CMGCs (canine mammary gland carcinomas). A, CMGCs grade I, collagen fibers in the stroma appear with red-orange birefringence (Coll-I) and green birefringence (Coll-III). B, CMGCs grade II, a predominance of Coll-I fibers can observe. C, CMGCs grade III, note the formation of dense collagen bands of Coll-I. D, Collagen fibers in pedunculated papillary structures in CMGCs, under low polarized light. PSR staining. 200X. 

Density of collagen type I and III in three grades of CMGCs. Coll-I (Collagen type I), Coll-II (Collagen type III). **** P < 0.0001.