ESR1 and cancer: The role of hormonal factors, specifically estrogen/estrogen receptor α (ER-α) had been hypothesized as the major contributing factor for this, as BRCA1 has ligand-dependent and independent transcriptional control over estrogen receptor.13, 14 However, tumor progression in BRCA1 defective condition could not be controlled by inhibiting estrogen receptors as majority of BRCA1 defective cancers are ER-α negative.15, 16, 17 In addition to estrogen and progesterone, hCG is known to be a critical factor for the development and differentiation of the breast tissue.