Differences in degree of lesion enhancement on CEM between ILC and IDC

OBJECTIVE: To investigate differences in the degree of enhancement on contrast-enhanced mammography (CEM) between patients with invasive lobular (ILC) and infiltrating ductal carcinoma (IDC) not otherwise specified. METHODS AND MATERIALS: Between 2010 and 2017, all patients diagnosed with ILC and who underwent CEM were included for this dual center study. Twenty-two patients with IDC, matched by size, were identified for comparison. Three independent readers, blinded for histopathology results, re-evaluated all CEM exams to determine degree of lesion enhancement according to a previously defined scoring scale ranging from minimal to strong enhancement. Interobserver agreement among the three readers was calculated by quadratic weighted κ coefficient. RESULTS: 44 patients were included: 22 patients with ILC and 22 patients with IDC. There were no significant differences in age, mean tumor size, tumor grade or receptor status between the two subgroups. Degree of lesion enhancement on CEM was more often considered weak in case of ILC compared to IDC according to two out of three readers (31.8% vs 4.5 %, p = 0.045 and 22.7 vs 4.5 %, p = 0.185). All other lesions showed moderate or strong enhancement. Interobserver agreement between the three independent readers was good (κ = 0.72). CONCLUSION: In patients with ILC, degree of lesion enhancement on CEM appears to be more often weak than in infiltrating ductal carcinoma not otherwise specified. Radiologists should be aware that weakly enhancing lesions may in fact be malignant and particularly invasive lobular cancers. ADVANCES IN KNOWLEDGE: Three independent readers evaluated 44 CEM cases with ILC or IDC. Degree of lesion enhancement seems more often weak in case of ILC. Radiologists should be aware of ILC in case of weak CEM enhancement.