Calcium oxalate crystals in breast biopsies. The missing microcalcifications.

Most calcifications detected by mammography and specimen radiography are readily identified by histologic sections stained with hematoxylin and eosin (H&E) or the von Kossa stain. However, calcifications composed of calcium oxalate crystals are not always seen in sections stained with H&E or with von Kossa. To study the incidence of calcium oxalate crystals in breast biopsies, we used polarized light microscopy to review 153 needle-localization breast biopsies. Birefringent crystals were observed in 19 cases (17 benign and 2 malignant), but typical calcium phosphate microcalcifications were revealed by H&E in only 16 of these 19 cases. Multiple H&E sections through the blocks of the remaining three cases did not reveal typical microcalcifications. These crystals did stain with silver nitrate/rubeanic acid with 5% acetic acid pretreatment but failed to stain with von Kossa and alizarin red at pH 4.2. This suggested that they were composed of calcium oxalate. Analytical electron microscopy performed in one of the three cases without typical microcalcifications demonstrated only a calcium peak of energy-dispersive x-ray analysis and an electron-diffraction pattern compatible with calcium oxalate monohydrate. We conclude that discrepancies between the amount of microcalcifications seen on the mammogram or on the x-ray film of the specimen or the paraffin blocks and the amount of microcalcifications seen on the H&E slides may be explained by the presence of calcium oxalate crystals. These crystals are detected with specimen radiography but are not easily seen on H&E slides unless polarized light microscopy is used. Polarized light microscopy and silver nitrate/rubeanic acid with 5% acetic acid pretreatment should be used for breast biopsy specimens when typical microcalcifications are not seen on H&E-stained sections.