Within the serine metabolic network, multiple members of the SLC family, including SLC1A4, SLC1A5, SLC6A14, and SLC12A4, collectively mediate cellular L‐serine uptake.[16, 17] Current evidence demonstrates that SLC1A5 serves as the predominant contributor to L‐serine uptake in breast cancer, whereas SLC6A14 plays a major role in colorectal cancer.[12, 18] SLC1A4 has been identified as the dominant transporter mediating L‐serine uptake in leukemia and at the blood‐brain barrier.[19, 20] However, the characterization of the principal L‐serine transporter in GC cells remains to be elucidated. Here, CCL21 is linked to breast cancer.