Second, unlike stromal cells (49, 50) and triple-negative breast cancers, which express high levels of GIV, ER+ breast cancer cells, such as MCF7 and T47D, lack GIV (51) due to an alternative splicing event (intron 19 retention) that leads to the loss of the resultant transcript to nonsense-mediated decay. Here, ESR1 is linked to breast cancer.