In 2009, Ruckhäberle et al. analyzed microarray data regarding GCS mRNA expression in 1,681 breast tumors and found that GCS expression was associated with positive estrogen receptor (ER) status, lower histological grading, low Ki67 levels and ErbB2 negativity (p<0.001 for all) [11]. This evidence concerns the gene ESR1 and breast neoplasm.