To identify the role of SWAP-70 in mouse breast cancer metastasis, we generated SWAP-70–deficient (KO) cell lines using the CRISPR/Cas9 system in the BALB/c-derived mouse breast cancer cell line 4T1, which resembles human metastatic triple-negative breast cancer cells (Dexter et al, 1978; Schrors et al, 2020). The gene discussed is SWAP70; the disease is breast cancer.