OBJECTIVE: To investigate the correlation of PDGF-BB and Ki-67 expressions with MRI features and levels of ER, PR, and HER-2 of patients with invasive ductal carcinoma (IDC) in different age groups. STUDY DESIGN: A total of 160 patients who were pathologically confirmed with IDC and who received biomarker testing and preoperative dynamic contrast- enhanced MRI scan at our hospital were recruited. They were divided into young age group (≤40 years, n=62) and middle to old age group (>40 years old, n=98). The expressions of PDGF-BB and Ki-67 in the cancerous and paracancerous tissues were detected by immunohistochemistry. RESULTS: The PDGF-BB and Ki-67 expressions in the cancerous tissues were significantly higher than those in the paracancerous tissues. There were significant differences between the age groups in the contrast enhancement pattern upon MRI and whether the lesion boundaries were smooth or not (p<0.05). However, dif- ferent age groups were not significantly different in the maximum tumor diameter, lesion shape features, and time signal intensity curve type (p>0.05). The PDGF-BB and Ki-67 expressions in the cancerous tissues were correlated with the levels of ER and PR, maximum tumor diameter, histological grade, and lesion shape features (p<0.05). Spearman’s correlation analysis indicated a positive correlation between PDGF-BB and Ki-67 expressions in the cancerous tissues (r=0.293, p=0.046). The tumor size varied significantly in pa- tients with low and high PDGF-BB and Ki-67 expressions (p<0.05). CONCLUSION: PDGF-BB and Ki-67 play a crucial role in the occurrence and development of IDC. The expressions of PDGF-BB and Ki-67 were correlated with other biomarkers and tumor diameter. However, their expressions were not correlated with other MRI manifestations except for tumor diameter. (Anal Quant Cytopathol Histpathol 2021;43:909-916) © Science Printers and Publishers, Inc. © 2021 Science Printers and Publishers Inc.. All rights reserved.