Collectively, these results show that Luminal A and TNBC breast cancer cells grown as 3D spheroids exhibit remarkably reduced cell viability upon long-term treatment with the pyrazinoylguanidine-type NHE1 inhibitor EIPA, but not with the benzoylguanidine-type inhibitor cariporide. This evidence concerns the gene SLC9A1 and breast carcinoma.