ESR2 and breast cancer: We further explored the intersection between obesity-associated systemic factors, SKBR3 cell ESR2 expression, and cell viability and growth by assessing the impact of the patient sera on these in vitro measures of breast cancer progression in our ESR2-overexpressing SKBR3 clones, which express equal levels of ESR2 following exposure to OB and N patient sera (Fig 3A).