PDE5A and breast cancer: We further calculated the prognostic risk score for each BC patient as follows: risk score = (0.0049 × expression level of PLOD1) + (0.0018 × expression level of CKB) + (0.0033 × expression level of PYGB) + (0.0031 × expression level of AKR1B1) + (0.0486 × expression level of PDE5A).