ELF3 and breast cancer: Furthermore, ELF3 knockdown in HCC1937 and SUM149PT cells, both of which are human breast cancer cell lines with BRCA1 mutations and allelic loss, also caused a significant decline in cell proliferation (Figure 4C and D, Figure 4—figure supplement 1B and C), suggesting that ELF3 is essential for BRCA1 mutant breast cancer cell survival.