High-resolution semiconductor 18F-FDG PET/CT with prone positioning for assessing the extent of mucinous breast carcinoma: initial experience

Objective: To assess the utility of high-resolution, semiconductor-based, ¹⁸ F-fluorodeoxyglucose ( ¹⁸ F-FDG) positron-emission tomography/computed tomography (PET/CT) with prone positioning for evaluating intramammary tumor extent in mucinous breast carcinoma. Methods: We retrospectively analyzed seven patients with pathologically confirmed mucinous breast carcinoma who underwent PET/CT without neoadjuvant chemotherapy between September 2020 and September 2024. A spherical volume of interest (VOI, 20 mm in diameter) was placed in the contralateral background fibroglandular breast tissue on PET images to assess background fibroglandular uptake (bFGU), from which the mean standardized uptake value (SUVmean) and standard deviation (SD) were derived. Four SUV thresholds were defined: SUVmean + 2 SD, SUVmean + 3 SD, 1.5 × SUVmean + 2 SD, and 1.5 × SUVmean + 3 SD. Tumor contours were delineated using semiautomatic software, and the maximum diameter was manually measured along the extracted contours at each threshold, followed by comparison with pathological tumor sizes and, in five cases, with magnetic resonance imaging (MRI)-based measurements. Results: All mucinous carcinomas were successfully detected by PET/CT. At the lowest threshold (SUVmean + 2 SD), the PET-based tumor size had the highest concordance with the pathological tumor size. Increasing threshold levels led to progressively greater underestimation of tumor size. The mean SUVmax values were 3.14 for tumors and 1.27 for bFGU. PET and MRI demonstrated comparable performance in all five cases in which both modalities were available. Conclusions: High-resolution ¹⁸ F-FDG PET/CT with prone positioning effectively delineated the extent of mucinous breast carcinoma, providing a diagnostic accuracy comparable to that of MRI. This technique may enhance preoperative planning for patients with this histological subtype.