The TERT promoter and PIK3CA were also the most frequently mutated sites regardless of cancer grade (Figure 4e,f); however, TP53 and ARID1A were less mutated in low-grade BC compared with high-grade BC (0% vs. 52.78% and 14.29% vs. 30.56%, respectively), which is consistent with previous studies [26,28]. Here, ARID1A is linked to breast cancer.