Predictive Value of 16α-[18F]-Fluoro-17β-Estradiol PET as a Biomarker of Progestin Therapy Resistance in Patients With Atypical Endometrial Hyperplasia and Low-Grade Endometrial Cancer

Nuclear Medicine and Molecular Imaging Applications in Gynecologic Malignancies: A Comprehensive Review

Gynecologic malignancies, consisting of endometrial, cervical, ovarian, vulvar, and vaginal cancers, pose significant diagnostic and management challenges due to their complex anatomic location and potential for rapid progression. These tumors cause substantial morbidity and mortality, often because of their delayed diagnosis and treatment. An estimated 19% of newly diagnosed cancers among women are gynecologic in origin. In recent years, there has been growing evidence supporting the integration of nuclear medicine imaging modalities in the diagnostic work-up and management of gynecologic cancers. The sensitivity of fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) combined with the anatomical specificity of computed tomography (CT) and magnetic resonance imaging (MRI) allows for the hybrid evaluation of metabolic activity and structural abnormalities that has become an indispensable tool in oncologic imaging. Lymphoscintigraphy, using technetium 99m (99mTc) based radiotracers along with single photon emission computed tomography/ computed tomography (SPECT/CT), holds a vital role in the identification of sentinel lymph nodes to minimize the surgical morbidity from extensive lymph node dissections. While not yet standard for gynecologic malignancies, promising therapeutic nuclear medicine agents serve as specialized treatment options for patients with advanced or recurrent disease. This article aims to provide a comprehensive review on the nuclear medicine applications in gynecologic malignancies through the following objectives: 1) To describe the role of nuclear medicine in the initial staging, lymph node mapping, response assessment, and recurrence/surveillance imaging of common gynecologic cancers, 2) To review the limitations of 18F-FDG PET/CT and promising applications of 18F-FDG PET/MRI in gynecologic malignancy, 3) To underscore the promising theragnostic applications of nuclear medicine, 4) To highlight the current role of nuclear medicine imaging in gynecologic cancers as per the National Comprehensive Cancer Network (NCCN), European Society of Surgical Oncology (ESGO), and European Society of Medical Oncology (ESMO) guidelines.

PET Imaging of Estrogen Receptors for Gynecological Tumors

ABSTRACT

In the past few decades, PET with 18F-FDG has been used for the diagnosis of gynecological malignancies and is considered to be superior to conventional imaging methods in diagnostic accuracy for detecting metastatic lesions and local recurrence and in evaluating the treatment response. On the other hand, several gynecological tumors, such as endometrial cancer and leiomyoma, and breast cancer are estrogen-dependent, in which estrogen is essential for their development and progression. 18F-FES is an 18F-labeled compound of estradiol, the most bioactive type of estrogen, and 18F-FES PET has been well-established for diagnosis, staging, and posttherapeutic follow-up in patients with estrogen receptor-positive breast cancer. Compared with in vitro assessment of tumor biopsy material, PET imaging has the advantages of being able to measure in vivo tumor behavior, characterize the entire tumor burden, and capture the heterogeneity of the tumor phenotype. In this article, we review the phenotyping of estrogen-related gynecological tumors other than breast cancer using 18F-FES PET and demonstrate the additional value of 18F-FES PET to 18F-FDG PET in their diagnosis and prognostication. Moreover, promising PET tracers other than 18F-FES and 18F-FDG for the evaluation of estrogen-related gynecological tumors are introduced.

Fatostatin reverses progesterone resistance by inhibiting the SREBP1-NF-κB pathway in endometrial carcinoma

Progesterone resistance can significantly restrict the efficacy of conservative treatment for patients with endometrial cancer who wish to preserve their fertility or those who suffer from advanced and recurrent cancer. SREBP1 is known to be involved in the occurrence and progression of endometrial cancer, although the precise mechanism involved remains unclear. In the present study, we carried out microarray analysis in progesterone-sensitive and progesterone-resistant cell lines and demonstrated that SREBP1 is related to progesterone resistance. Furthermore, we verified that SREBP1 is over-expressed in both drug-resistant tissues and cells. Functional studies further demonstrated that the inhibition of SREBP1 restored the sensitivity of endometrial cancer to progesterone both in vitro and in vivo, and that the over-expression of SREBP1 promoted resistance to progesterone. With regards to the mechanism involved, we found that SREBP1 promoted the proliferation of endometrial cancer cells and inhibited their apoptosis by activating the NF-κB pathway. To solve the problem of clinical application, we found that Fatostatin, an inhibitor of SREBP1, could increase the sensitivity of endometrial cancer to progesterone and reverse progesterone resistance by inhibiting SREBP1 both in vitro and in vivo. Our results highlight the important role of SREBP1 in progesterone resistance and suggest that the use of Fatostatin to target SREBP1 may represent a new method to solve progesterone resistance in patients with endometrial cancer.

The quest for improving the management of breast cancer by functional imaging: The discovery and development of 16α-[18F]fluoroestradiol (FES), a PET radiotracer for the estrogen receptor, a historical review

INTRODUCTION

16α-[18F]Fluoroestradiol (FES), a PET radiotracer for the estrogen receptor (ER) in breast cancer, was the first receptor-targeted PET radiotracer for oncology and is continuing to prove its value in clinical research, antiestrogen development, and breast cancer care. The story of its conception, design, evaluation and use in clinical studies parallels the evolution of the whole field of receptor-targeted radiotracers, one greatly influenced by the research and intellectual contributions of William C. Eckelman.

METHODS AND RESULTS

The development of methods for efficient production of fluorine-18, for conversion of [18F]fluoride ion into chemically reactive form, and for its rapid and efficient incorporation into suitable estrogen precursor molecules at high molar activity, were all methodological underpinnings required for the preparation of FES. FES binds to ER with very high affinity, and its in vivo uptake by ER-dependent target tissues in animal models was efficient and selective, findings that preceded its use for PET imaging in patients with breast cancer.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Comparisons between ER levels measured by FES-PET imaging of breast tumors with tissue-specimen ER quantification by IHC and other methods show that imaging provided improved prediction of benefit from endocrine therapies. Serial imaging of ER by FES-PET, before and after dosing patients with antiestrogens, is used to determine the efficacious dose for established antiestrogens and to facilitate clinical development of new ER antagonists. Beyond FES imaging, PET-based hormone challenge tests, which evaluate the functional status of ER by monitoring rapid changes in tumor metabolic or transcriptional activity after a brief estrogen challenge, provide highly sensitive and selective predictions of whether or not there will be a favorable response to endocrine therapies. There is sufficient interest in the clinical applications of FES that FDA approval is being sought for its wider use in breast cancer.

CONCLUSIONS

FES was the first PET probe for a receptor in cancer, and its development and clinical applications in breast cancer parallel the conceptual evolution of the whole field of receptor-binding radiotracers.

Prognostic Value of 16α-18F-Fluoro-17β-Estradiol PET as a Predictor of Disease Outcome in Endometrial Cancer: A Prospective Study

The purpose of this study was to evaluate the potential of 16α-¹⁸F-fluoro-17β-estradiol (¹⁸F-FES) PET to predict prognosis in patients with endometrial cancer (EC). Methods: In total, 67 patients with International Federation of Gynecology and Obstetrics (FIGO) stage I-IV EC underwent ¹⁸F-FES and ¹⁸F-FDG PET/CT before treatment. The SUV_mean of the primary tumor was compared with the clinical characteristics, and the relationships between SUV and progression-free survival (PFS) or overall survival were analyzed. Results: ¹⁸F-FES SUV was significantly associated with stage, histology, lymphovascular space involvement (LVSI), and lymph node metastasis, and ¹⁸F-FDG SUV was significantly associated with stage, myometrial invasion, tumor size, and lymph node metastasis. Receiver-operating characteristic curve analysis revealed that ¹⁸F-FES SUV could significantly detect tumor progression and survival, with areas under the curve of 0.813 and 0.790, respectively, whereas ¹⁸F-FDG SUV could detect them with areas under the curve of 0.557 and 0.635, respectively. The Kaplan-Meier survival curve showed that patients with a low ¹⁸F-FES SUV had significantly poor PFS (P < 0.001) and overall survival (P = 0.001) compared with patients with a high SUV, whereas ¹⁸F-FDG showed no significant differences. In a subanalysis of 27 patients with a low risk of recurrence (FIGO stage IA endometrioid carcinoma [grade 1 or 2] without LVSI), those with a low ¹⁸F-FES SUV also had poorer PFS than those with a high SUV (P = 0.002). In multivariate analysis, an ¹⁸F-FES SUV of less than 2.63 (P = 0.037; hazard ratio, 10.727; 95% CI, 1.16-99.35) and FIGO stages III and IV (P = 0.042; hazard ratio, 8.838; 95% CI, 1.09-71.84) were significantly associated with PFS. Conclusion: A low ¹⁸F-FES for the primary tumor was strongly associated with prognostic factors of EC such as LVSI and lymph node metastasis, and a low ¹⁸F-FES SUV was an independent prognostic factor for PFS in patients with EC. These data suggest that pretreatment ¹⁸F-FES PET might be useful in determining the appropriate treatment for patients with EC.