Background: This study is aimed at investigating the correlation between apparent diffusion coefficient (ADC) values obtained from diffusion-weighted imaging (DWI) and prognostic factors in breast cancer. We hypothesized that lower ADC values would be observed in more aggressive tumors, including those with higher histological grades and Ki-67 expression levels. A retrospective analysis was conducted on patients with malignant breast lesions who underwent breast magnetic resonance imaging (MRI), including DWI sequences, at our center between January 2022 and January 2023. MRI was performed on a 1.5 T scanner using a bilateral phased-array eight-channel breast coil. ADC values were calculated utilizing b values of 400 and 800 s/mm² and evaluated in relation to prognostic factors, including age, tumor size, tumor grade, lymph node involvement, Ki-67 proliferation index, estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status.

Results: This study included 88 patients with 89 malignant lesions. ADC values showed no significant association with age, tumor size, histological type, lymph node involvement, or receptor status (ER, PR, and HER2). However, tumors with higher Ki-67 expression exhibited significantly lower median ADC values. For Ki-67 thresholds of ≥ 14% and ≥ 30%, p values were 0.02 and < 0.01, respectively. A negative correlation between ADC values and the Ki-67 index was noted (p = 0.01, ρ = -0.28). Additionally, Grade I tumors had higher ADC values than Grade II and III tumors (p < 0.01), while no difference was observed between Grade II and III tumors (p = 0.61).

Conclusion: Lower ADC values correlate with higher tumor grades and Ki-67 expression, suggesting their potential role as imaging biomarkers for assessing breast cancer aggressiveness.