SLC9A1 and breast cancer: However, as summarized in Figure 11, it is clear from our analyses that NBCn1 and NHE1 have very different consequences in human breast cancer tissue: Na+,HCO3– cotransport sets the steady-state pHi associated with proliferative activity (Figure 7G); and the capacity for Na+,HCO3– cotransport and protein expression of NBCn1 predict lymph node metastasis (Figure 8G).