Specifically, our inverse variance weighted (IVW) analysis indicated that high expression of cathepsin F is associated with an increased risk of in situ breast cancer (IVW: p = 0.031, OR = 1.190, 95% CI = 1.016–1.394) (Figure 2B), whereas high expression of cathepsin E is associated with an increased risk of malignant breast tumors (IVW: p = 0.006, OR = 1.103, 95% CI = 1.028–1.184), including both HER2-positive (IVW: p = 0.047, OR = 1.092, 95% CI = 1.001–1.191) and HER2-negative (IVW: p = 0.016, OR = 1.089, 95% CI = 1.016–1.166) breast cancers (Figure 2A). Here, CTSF is linked to breast carcinoma in situ.