Gene copy number variations (CNVs) analysis showed amplification of PIK3CA in 8.1%, EGFR in 6.8% and CCND1 in 16% of MBCs, whereas deletion of ESR1 was detected in 15% of MBCs.
Furthermore, the high frequency of hormone receptor positivity and the association between ER positivity and CCND1 overexpression supports the notion that hormonal regulation is likely to be essential for the development of MBC.