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Previous studies had shown that SNPs at a locus on chromosome 6 are associated risk of breast cancer; the aim of this study was to identify the causative genetic variant within this region and understand how it influences risk of oestrogen receptor α-positive (ER+ve) breast cancer.

In order to identify genes that were correlated with the ESR1 gene, mRNA in tumour samples from 104 women with ER+ve breast cancer were analysed. Gene expression data from publicly available normal and breast cancer datasets were used to validate findings, and the biological effects of relevant genes were investigated further by manipulating their expression in cell cultures.

The levels of three genes (C6ORF96, C6ORF97, and C6ORF211) were correlated with ESR1 expression both before and after treatment with oestrogen synthesis inhibitors. Investigation of the function of these genes showed that C6ORF211 promotes proliferation (growth) of cultured cells, and is correlated with proliferation in breast tumours, whereas C6ORF97 inhibits proliferation.

Although these genes are linked to the oestrogen receptor, their behavior is independent of it, suggesting that they may mediate or modify its biological effects. They may also act in conjunction with SNPs in this region to influence breast cancer risk; however, this has yet to be established. The exact biological relationship between ESR1 and these genes is yet to be discovered, but they could be potential targets for future therapies.

Breast cancer is the most common cancer in women in the UK and an understanding of the biological factors involved is important in directing existing treatments and developing new ones. This study identifies new factors that may play a role in the disease, but further work is needed to understand their exact role in breast cancer and their potential as targets for therapy.