Histomorphological evaluation of stromal collagen in canine mammary tumours: A study using picrosirius red stain and polarizing microscopy

Mammary gland tumours are considered as the most common neoplasms in sexually intact female dogs. Incidence of mammary tumours, especially the malignant ones are found to be rare in dogs younger than five years of age. Latest reports indicate that more than 75 per cent of canine mammary tumours (CMTs) are of malignant type. Recent research has demonstrated that in breast cancer, apart from changes in the parenchyma, major modifications also occur in the stroma or tumour microenvironment, which surrounds the neoplastic cells and these changes are now understood to be crucial factors in the onset and progression of tumour. The tumour microenvironment consists of multiple cell types such as fibroblasts, leukocytes, adipocytes, myoepithelial cells, endothelial cells and the extra cellular matrix (ECM). Numerous studies have indicated that the primary protein in the ECM, collagen, has the potential to give physical, biochemical, and biomechanical impulses to both tumour and non-tumour cells, thus regulating the growth and spread of cancer. The current study employed special staining using picrosirius red to demonstrate the stromal collagen in CMTs and utilised polarised microscopy to analyse the birefringence of collagen fibres in tumours. Picrosirius red staining for evaluation of alterations in stromal collagen fibres was identified to be highly efficient in determining the prognosis of CMTs.