Here, we treated the BRCA1 exon 11 mutant SUM149PT breast cancer cells and their complemented derivative expressing wild-type BRCA1 (SUM149PT + BRCA1) with the PARPi olaparib for 1 h, a previously established condition that promotes ssDNA gap formation (Simoneau et al. 2021). This evidence concerns the gene BRCA1 and breast cancer.