SIRT4 and breast cancer: Glutamine is an essential nutrient for cell growth and viability, and tamoxifen suppresses the proliferation of ER‐negative cells through the inhibition of glutamine uptake.5, 9 To examine if tamoxifen also reduces glutamine uptake in ER‐positive breast cancer cells and if its efficacy is affected by SIRT4, we measured glutamine levels in the medium of MCF7 and T47D cells for 3 days after SIRT4 overexpression and tamoxifen treatment.