Mammary microcalcifications in breast cancer: simple bystanders or active phenomenon mediated by epithelial to mesenchymal transition?
AbstractMammary microcalcifications have a crucial role in breast cancer detection, but the
processes that induce their formation are unknown. Moreover, recent studies have
described the occurrence of the epithelial–mesenchymal transition (EMT) in breast
cancer, but its role is not defined. In this study, we hypothesized that epithelial cells
acquire mesenchymal characteristics and become capable of producing breast
microcalcifications. Moreover, we wanted to further investigate the evolution of the
breast lesions with microcalcifications hypothesizing and investigating a pathological
mechanism able to describe this phenomenon.
Breast sample biopsies with microcalcifications underwent energy dispersive X-ray
microanalysis to better define the elemental composition of the microcalcifications.
Images by mammographic exams were used to extrapolate pixel-wise values of
density-related microcalcification features.
Breast sample biopsies without microcalcifications were used as controls. The
ultrastructural phenotype of breast cells near to calcium deposits was also
investigated to verify EMT in relation to breast microcalcifications. The mesenchymal
phenotype and tissue mineralization were studied by immunostaining for vimentin,
BMP-2, β2-microglobulin, β-catenin and osteopontin (OPN).
The complex formation of calcium hydroxyapatite was strictly associated with
malignant lesions whereas calcium-oxalate is mainly reported in benign lesions.
Notably, for the first time, we observed the presence of magnesium-substituted
hydroxyapatite, which was frequently noted in breast cancer but never found in
benign lesions. In the 69% of the cases, Mg-Hap wasradiologically detectable as the
“casting type” microcalcification. Moreover, pixel measured in correspondence to
microcalcifications revealed that Mg-HAp microcalcifications were significantly more
radiodense than those made of HA and CO.
Morphological studies demonstrated that epithelial cells with mesenchymal
characteristics were significantly increased in infiltrating carcinomas with
microcalcifications and in cells with ultrastructural features typical of osteoblasts
close to microcalcifications. These data were strengthened by the rate of cells
expressing molecules typically involved during physiological mineralization (i.e.
BMP-2, OPN) that discriminated infiltrating carcinomas with microcalcifications from
those without microcalcifications.
We found significant differences in the elemental composition of calcifications
between benign and malignant lesions. Observations of cell phenotype led us to
hypothesize that under specific stimuli, mammary cells, which despite retaining a
minimal epithelial phenotype (confirmed by cytokeratin expression), may acquire
some mesenchymal characteristics transforming themselves into cells with an
osteoblast-like phenotype, and are able to contribute to the production of breast microcalcifications