Calcium oxalate in breast lesions biopsied for calcification detected in screening mammography: incidence and clinical significance.

Two types of calcification have been reported in breast tissue: one appears as dark-blue deposits in routine histologic tissue sections and has been found to be composed mostly of calcium phosphate (CaP); the other is colorless and represents calcium oxalate (CaOx). CaP has been well characterized, but little is known about CaOx. The presence of CaOx was evaluated in 91 breast lesions (71 retrospective and 20 prospective cases) biopsied for the presence of calcification in screening mammography. CaOx was found in 36 cases (39%). CaOx is usually not clearly visible in routine histologic sections. CaOx is found as refractile, strongly birefringent crystals with characteristic morphology. CaOx was present only within benign lesions which frequently showed apocrine metaplasia. However, the breast tissue away from the areas with CaOx displayed a morphologic spectrum roughly similar to that in cases with CaP only. CaOx was clinically significant, i.e., actually represented the mammographic calcification, for which the biopsy was performed in 12% (11/91) of all cases studied and in 31% (11/36) of cases in which CaOx was found. In the cases where CaOx was not considered clinically significant, it was either not radiographically visible or, if visible, did not definitely represent the mammographic calcification for which the biopsy was performed. Since CaOx in breast biopsies is often clinically significant, and since CaOx is not clearly visible in routine sections, examination under polarized light is suggested for all breast biopsies removed for mammographic calcification, particularly when CaP deposits corresponding to the mammographic calcification are not apparent.