Evaluation of a ductal carcinoma in situ component accompanying HER2-positive invasive breast cancer on contrast-enhanced mammography

Objectives: A DCIS component can be present accompanying HER2+ invasive breast cancer (IBC) in approximately 57 % of patients. Until now, no contrast-enhanced mammography (CEM) studies have investigated the detection of a DCIS component, which is important for surgical decision-making. This study aimed to investigate imaging findings of a DCIS component in HER2+ IBC on CEM. Methods: Women with HER2+ IBC with a DCIS component that underwent CEM between 2013-2021 were included. Two independent radiologists retrospectively reassessed CEM exams, and a breast pathologist reassessed histopathology specimen. The percentage and extent of suspicious calcifications and non-mass enhancement (NME) on CEM, and interobserver agreement between radiologists was determined. In the primary surgery group, the detection rate of DCIS outside of the invasive tumor was determined, and maximum diameter of imaging findings was compared to histopathology. Results: Sixty-two patients were included. CEM showed suspicious calcifications (27.4 %), NME (16.1 %), both (27.4 %) or no findings (29.0 %), related to DCIS. In the primary surgery group (n = 45), CEM detected 27 of 35 DCIS components present outside of the invasive tumor (77.1 %). NME was a better predictor for DCIS diameter (ICC = 0.65) compared to suspicious calcifications (ICC = 0.43). Inter-observer agreement on detection of imaging findings was better for suspicious calcifications (kappa = 0.81) compared to NME (kappa = 0.47), while reliability between size measurements was comparable (ICC = 0.89 versus ICC = 0.80, respectively). Conclusion: CEM was able to detect 77.1% of DCIS present outside of the invasive tumor. NME is the most accurate predictor of DCIS diameter, but requires improvements regarding inter-observer agreement.