Correlation of Radiological and Pathological Tumor Sizes in Breast Cancer Based on Molecular Subtypes and Accompanying DCIS: A Retrospective Multicenter Study

Purpose: This study aims to compare radiological tumor sizes obtained by mammography (MMG), ultrasonography (US), and magnetic resonance imaging (MRI) with pathological sizes to determine if molecular subtypes and the presence of accompanying ductal carcinoma in-situ (DCIS) affect accuracy. Methods: A total of 559 cases diagnosed with breast cancer in 11 different centers between 2010–2023 were included in the study. The patients' MMG, US, and MRI images were re-evaluated, and radiological findings and tumor sizes were recorded. Histological diagnosis (invasive/in-situ/mixed), receptor status, Ki-67 index, and tumor size were recorded from the pathology reports. Pathologic tumor size (pT) was accepted as the gold standard. Results: The mean pT was 21.1±14.9 (2.7–100) mm in Luminal A tumors, 20.6±12.6 (2–70) mm in Luminal B tumors, 26.3±14.7 (6–80) mm in HER-2(+) tumors, 26.3±14.7 (8–125) mm in triple (-) (TN) tumors. The highest agreement in invasive tumors was obtained with MRI (MRI r:0.831, US r:0.769, MMG r:0.650). In DCIS cases, the agreement was strong with MRI (r:0.770) and intermediate with MMG and US (r:0.517 and r:0.593, respectively). In mixed tumors, agreement was strong with MRI (r:0.817), intermediate with US (r:0.656), and low with MMG (r:0.499). Based on molecular subtypes, MRI had a strong correlation (r>0.7) in both invasive and mixed tumors of all subtypes. US had a strong correlation in all invasive tumors (r>0.7). The correlation was intermediate in Luminal mixed tumors. Mammography had a strong correlation only in invasive Luminal A tumors (r>0.7), and an intermediate correlation in the other invasive tumor subtypes. Regarding mixed tumors, its correlation level was intermediate in Luminal B and TN tumors, and low in Luminal A and HER-2(+) tumors. Conclusion: This multicenter study shows that MRI is the most reliable method for determining preoperative tumor size of invasive and in-situ tumors and all molecular subtypes. The correlation levels of all modalities decreased in pure and mixed DCIS cases, however the difference was minimal with MRI.