Purpose: To evaluate a possible correlation between apparent diffusion coefficient (ADC) value and tumor-infiltrating lymphocytes (TILs) level in breast cancer (BC). A second objective was to assess whether there were other histopathologic features that could affect mean ADC value.
Methods: In this 4-year retrospective study were included 125 patients who underwent radical or modified mastectomy for monofocal BC. All subjects had performed preoperative MRI with the same 1.5-T machine and protocol, which consisted of STIR, DWI and DCE sequences. Based on TIL score, BCs were stratified into two groups: absent-low TIL (≤ 10%) and medium-high TIL (> 10%). The t test was used to correlate mean ADC value with TIL groups. Receiver operating characteristic curve and Youden index were used in order to identify ADC value threshold to distinguish the two TIL groups.
Results: BC patients with absent-low TIL level and medium-high TIL one were, respectively, 66 (52.8%) and 59 (47.2%). Mean ADC value was 1.05 ± 0.19 * 10-3 mm2 s-1. Absent-low TIL group showed a lower mean ADC value than medium-high TIL one (0.96 ± 0.18 * 10-3 mm2 s-1 vs 1.14 ± 0.16 * 10-3 mm2 s-1; p < 0.0001). ADC value threshold in order to distinguish the two TIL groups with maximum sensitivity (67.8%) and specificity (80.3%) was 1.03 * 10-3 mm2 s-1. ADC value was shown to be significantly related to TILs level (p < 0.0001) and cancer histotype (p = 0.0006), with a lower mean ADC value correlated to absent-low TIL level and ductal histotype.
Conclusion: BCs with absent-low TIL showed a statistically significant lower mean ADC value than those with medium-high TIL. ADC value threshold in order to distinguish these two groups was 1.03 * 10-3 mm2 s-1.
Keywords: ADC; Breast cancer; MRI; TIL.