Carbonate and cation substitutions in hydroxylapatite in breast cancer micro-calcifications

Calcification within breast cancer is a diagnostically significant radiological feature that generally consists of hydroxylapatite. Samples from 30 cases of breast carcinoma with calcification were investigated using optical microscopy, energy-dispersive X-ray analysis, transmission-electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, synchrotron radiation X-ray diffraction and X-ray fluorescence. Under optical microscopy, the calcifications were found to consist of either irregular aggregates with widths >200 µm or spherical aggregates similar to psammoma bodies with an average diameter of 30 µm. Transmission-electron microscopy showed that short columnar or dumbbell-shaped crystals with widths of 10-15 nm and lengths of 20-50 nm were the most common morphology; spherical aggregates (∼1 µm in diameter) with amorphous coatings of fibrous nanocrystals were also observed. Results indicated that hydroxylapatite was the dominant mineral phase in the calcifications, and both CO32- and cation substitutions (Na, Mg, Zn, Fe, Sr, Cu and Mn) were present in the hydroxylapatite structure. Fourier-transform infrared spectra show peaks at 872 and 880 cm-1 indicating that CO32- substituted both the OH- (A type) and PO43- (B type) sites of hydroxylapatite, making it an A and B mixed type. The ratio of B- to A-type substitution was estimated in the range of 1.1-18.7 from the ratio of peak intensities (I872/I880), accompanied with CO32- contents from 1.1% to 14.5%. Trace arsenic, detected in situ by synchrotron radiation X-ray fluorescence was found to be distributed uniformly in the calcifications in the form of AsO43- substituting for PO43-. It is therefore proposed that identifying these trace elements in breast cancer calcifications may be promising for future clinical diagnostics.