Solid papillary breast carcinoma with mucinous differentiation

A case is reported of a solid variant of infiltrating papillary carcinoma of the breast with mucinous differentiation in a 74-year-old woman. Macroscopically, the tumor was solid and lobular, 4.5 cm in diameter. Light microscopy showed solid papillary invasive carcinoma mixed with infiltrating ductal carcinoma, not otherwise specified. Abundant intracellular and extracellular acid mucin produced by the solid papillary tumor cells was proven histochemically by: PAS, PAS-D, mucicarmine and alcian blue. Immunohistochemically, the papillary carcinoma cells were strongly reactive to estrogen receptors, and weakly to moderately reactive to smooth muscle actin. We suggest that papillary carcinoma of the breast could have potentially high degree of aggressiveness, and that differential diagnosis of these rare tumors might be a histopathological problem.