In paired patient samples, OXCT1 (log2FC = -1.41), SHMT1 (log2FC = -1.31), and ACAT1 (log2FC = -1.07) were significantly downregulated in ER+ tumors relative to matched normal tissue (adjusted p < 0.001 for all three).<h4>Conclusions</h4>ER+ breast cancer cell lines show heterogeneous metabolic responses to BHB supplementation under glucose restriction. The gene discussed is SHMT1; the disease is breast cancer.