Abstract P3-01-02: Oxalate microcalcifications induce breast cancer tumors
Authors: Gil GA , Castellaro AM , Pucci O , Tonda A , Cejas H , Caputto BL 
Published: August 2014

One shared characteristic of breast cancer is the appearance of mammographic upon mammography examination. Microcalcifications are routinely used to detect breast cancer in its early stages, which is of key importance due to the possibility that early detection gives for the application of more conservative therapies and for a better patient outcome. Mammary microcalcifications are composed of calcium oxalate or calcium phosphate. Oxalate has been considered as an inert end product of the metabolism. However, its accumulation is thought to be toxic to living tissues because it induces some pathological circumstances. Several results support the hypothesis that Oxalates are a secretion product that is produced by many kinds of cells, including apocrine cells, kidney cells and liver cells, among others. Exposure of renal epithelial cells to oxalate leads to diverse events that include, among others, induction of immediate early genes (IEG) expression, re-initiation of DNA synthesis, cell growth, and up or down-regulation of more than 1000 genes.

Not enough research has been carried out directed to investigate the impact the presence of oxalates has within the breast tumor microenvironment. Neither are the interactions between oxalates breast-epithelial cells nor the signal transduction pathways involved in it, well understood.

Herein, we have obtained good evidence showing that oxalates excreted from apocrine cells induce alterations in normal breast epithelial cells, and that the exposure of breast epithelial cells to excreted oxalate in a chronic way, sets the stage for transformation from normal to fully developed breast tumors.

Oxalate induces DNA synthesis and IEG overexpression in MCF7 and MDAMB231 human breast cancer cells in culture. When these cells were treated with oxalate, the IEG c-Fos and Fra-1 were over-expressed as determined by Western Blot. Additionally, in human breast cancer tissues we found a strict correlation between oxalate concentration and overexpression of c-Fos and Fra-1. Paired adjacent non-tumor tissues linked with the tumor tissues have neither high levels of oxalate nor c-Fos/Fra-1 over-expression.

Two groups of female mice (n = 20 each) periodically received an injection of oxalate or of saline solution (controls) into a mammary fatpad during a month. Surprisingly, the mice that were injected with oxalate generated very aggressive tumors. c-Fos and Fra-1 were also found over-expressed in these tumors. Furthermore, the final oxalate concentrations in the mice tumors were analogous to those found in the human breast tumor tissues whereas oxalate was almost undetectable in the non-pathological control tissues. Mice breast tumors were palpable within three months in 18/20 of oxalate treated as compared to the 0/20 control animals. Eight tumors were very aggressive and showed very fast growth rates; in these tumors, it was possible to appreciate high rate of atypical mitosis upon haematoxylin/eosin staining. Five tumors were very invasive and were found multi-localized in all breast areas. These five tumors also showed an atypically high mitotic rate, big pleomorphic nuclei, and macro and multi nucleoli. We expect that if we can control oxalic production or even better, control their action, we will significantly reduce the development of human breast cancers.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-01-02.