Many studies have pointed out that PDE4D is a tumor-promoting molecule in some cancers, including hematological malignancies, lung cancer, prostate cancer, colorectal cancer, gastric cancer, melanoma, head and neck cancer, breast cancer, ovarian cancer, endometrioma, pancreatic ductal adenocarcinoma (PDAC), etc. [1–5]. The gene discussed is PDE4D; the disease is breast cancer.