Abstract P6-01-04: Initial experience of dedicated breast PET imaging of ER+ breast cancers using [F-18]fluoroestradiol
Authors: Jones EF , Ray KM , Mukhtar R , Li W , Franc BL , Esserman LJ , Joe BN , Pampaloni MH , Hylton NM 
Published: May 2019

Abstract
Introduction: Breast cancer is a heterogeneous disease encompassing distinct subtypes with variable treatment response, relapse risk and overall prognosis. The majority of breast cancers are estrogen receptor-positive (ER+). While neoadjuvant endocrine therapy trials have been proposed to better identify therapeutic approaches for ER+ breast cancer, accurate quantification of the ER biomarker is necessary to assess the primary tumor and its likelihood of response to treatment.
Dedicated breast positron emission tomography (dbPET) is an emerging technology with a high spatial resolution that enables detection of sub-centimeter lesions and depiction of intratumoral heterogeneity. In this study, we report our initial experience with [F-18]fluoroestradiol (FES) dbPET in assessing ER+ primary breast cancers.
Materials and Methods: In an IRB-approved protocol, patients with biopsy-confirmed ER+ breast cancers were imaged with dbPET (MAMMI, OncoVision, Valencia, Spain) as a companion diagnostic tool to standard breast MRI. A dose of 5 mCi of FES was administered and patients were imaged in the prone position at 45 min post-injection. As part of routine clinical care, MR images were reviewed by a certified breast radiologist experienced in breast MRI. DbPET was reviewed by a radiologist specialized in nuclear imaging.
Results: Five patients with ER+ breast cancers were imaged. Patient ages ranged from 33 to 64. Two patients with infiltrating lobular carcinomas measuring up to 6.7 cm and 5.3 cm at MRI demonstrated corresponding FES tumor-to-normal maximum standard uptake value (SUVmax) ratio at 4.81 and 2.49 respectively. A third patient demonstrated multifocal FES uptake corresponding to multifocal invasive ductal carcinoma and ductal carcinoma in situ with disease foci ranging from 9-13 mm. In this patient, the more posterior disease foci seen on MRI were excluded from the field of view of dbPET. One patient demonstrated an absence of FES uptake in her 3.4 cm infiltrating ductal carcinoma, which was due to estrogen receptor blockade from the recent administration of tamoxifen for a fertility preservation procedure. The final patient had metastatic cervical and axillary lymphadenopathy secondary to a breast primary that was occult on mammography and MRI. FES-dbPET also showed no corresponding uptake in the ipsilateral breast, possibly due to the small size of the primary lesion and/or low tumor to background uptake ratio.
Conclusions: FES-dbPET imaging has potential as a diagnostic tool that is complementary to MRI in characterizing ER+ primary breast cancers. Limitations include variations of FES uptake in different ER+ breast cancer diseases and exclusion of posterior breast tissue near the chest wall and the axillary regions. However, FES-dbPET has a high potential for clinical utility, especially in measuring response to neoadjuvant endocrine treatment. Further development to improve the dbPET field of view and studies with a larger cohort of ER+ breast cancer patients are therefore warranted.
Citation Format: Jones EF, Ray KM, Mukhtar R, Li W, Franc BL, Esserman LJ, Joe BN, Pampaloni MH, Hylton NM. Initial experience of dedicated breast PET imaging of ER+ breast cancers using [F-18]fluoroestradiol [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-01-04.