Recent advances in nuclear medicine in endocrine oncology

The clinical signification and application value of [68Ga]Ga-PSMA imaging in thyroid malignancy

PURPOSE

Approximately 5% of differentiated thyroid cancers lose the ability to uptake iodine, leading to limited treatment options and poor prognosis due to invasion and distant metastasis. PSMA imaging probes have been proposed as a potential diagnostic and therapeutic tool for iodine-refractory thyroid cancer. However, there are limited reports and significant heterogeneity in patient selection, warranting further exploration of the application value of PSMA in thyroid cancer.

METHODS

We performed Western Blot, PCR, and [68Ga]Ga-PSMA uptake experiments on cell lines and conducted in vivo small animal imaging. Clinical and radiological results of included differentiated thyroid cancer patients were collected. (Trial registration number: 2021-669, Trial registration date: December 30, 2021).

RESULTS

PSMA expression levels were significantly higher in poorly differentiated thyroid cancer (7.86 ± 1.90 vs. 1.00 ± 0, P < 0.01; 7.86 ± 1.90 vs. 0.03 ± 0.02, P < 0.01), but [68Ga]Ga-PSMA imaging correlated with tumor burden, such as 18F-FDG (8.08 ± 7.74 and 5.67 ± 4.23, P = 0.01) and Tg levels (307.1 ± 183.4 vs. 118.0 ± 116.1, P = 0.002).

CONCLUSION

Our results showed that PSMA expression increased with the decrease of thyroid cancer differentiation. However, the level of [68Ga]Ga-PSMA uptake in thyroid cancer patients was not significantly associated with the degree of thyroid cancer differentiation, but also with the metabolism and burden of tumors such as 2-[18F]FDG and Tg levels. These findings provide additional clinical significance and application value for PSMA in thyroid cancer.

Prognostic and predictive value of nuclear imaging in endocrine oncology

In the last few years, the role and use of medical technologies in (neuro)endocrine oncology has greatly evolved allowing not only important diagnostic information but also prognostic stratification in different clinical situations. The terms "prognostic" and "predictive" are commonly used to describe the relationships between biomarkers and patients' clinical outcomes but have quite different meaning. The present work discusses the prognostic and predictive value of nuclear medicine imaging. It critically reviews the clinical significance and potential impact of molecular examinations on follow-up and therapeutic strategies in patients with neuroendocrine neoplasms, thyroid tumors, and adrenal malignancies.

PSMA expression level predicts differentiated thyroid cancer aggressiveness and patient outcome

Background

Prostate-specific membrane antigen (PSMA) is overexpressed on the endothelial cells of tumor neo-vessels of several solid malignancies, including differentiated thyroid cancer (DTC). We aimed to test the potential role of PSMA as a biomarker for DTC aggressiveness and outcome prediction.

We retrospectively screened all patients who underwent thyroidectomy between 1 January 2010 and 31 December 2017 in our institution. Applying the inclusion (histological diagnosis of thyroid cancer and tissue availability) and exclusion criteria (no clinical or follow-up data or diagnosis of medullary thyroid cancer), a cohort of 59 patients was selected. The monoclonal mouse anti-human PSMA antibody was used to stain tissue sections. A 3-point scale was used to score PSMA positivity: 0–5% expression was considered as negative (score 0), 6–50% as moderately positive (score 1), and 51–100% as highly positive (score 2). A cumulative score (0–10%, 11–79%, and 80–100%) was also explored. Univariate and multivariate logistic regression analyses were performed to predict the presence of distant metastases, chosen as endpoint of aggressiveness. The area under the curve (AUC) was calculated. Cox models were built to predict patient outcome in terms of recurrence, iodine refractoriness, and status at last follow-up, which were calculated using the Kaplan-Meier failure function.

Results

At immunostaining, 12, 25, and 22 patients had scores of 0, 1, and 2, respectively. According to the cumulative score, PSMA expression was ≤ 10% in 17 cases, 11–79% in 31 cases, and ≥ 80% in 11 cases. At multivariate analysis, age, sex, histotype, vascular invasion, T and N parameters, and PSMA positivity were significant predictors of distant metastases. The AUC was 0.92. Recurrence or progression occurred in 19/59 patients. Twelve patients developed radioiodine (RAI) refractoriness, after a median time of 17 months (range 2–32). One patient died of DTC; 46 of the 58 patients alive at last follow-up were disease free. Median DFS was 23 months (range 3–82). The final multivariate model to predict RAI refractoriness included as covariates the stage, high PSMA expression (≥ 80%), and the interaction between moderate PSMA expression (11–79%) and stage.

Conclusions

PSMA, a marker of neovasculature formation expressed by DTC, contributes in the prediction of tumor aggressiveness and patient outcome.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0559-9) contains supplementary material, which is available to authorized users.

68Ga-PSMA PET thyroid incidentalomas

INTRODUCTION

Thyroid incidentaloma is defined as a thyroid lesion incidentally and newly detected by imaging techniques performed for an unrelated purpose and especially for a non-thyroid disease. The aim of this review is to evaluate the prevalence and clinical significance of focal incidental radiolabelled prostate-specific membrane antigen (PSMA) uptake in the thyroid gland [PSMA thyroid incidentaloma (PTI)] revealed by PET/CT or PET/MRI.

METHODS

A comprehensive literature search of the PubMed/MEDLINE, Scopus, and Embase databases was conducted to find relevant published articles about the prevalence and clinical significance of PTIs detected by PET/CT or PET/MRI in patients studied for other oncologic purposes.

RESULTS

Twelve articles were included in the systematic review. Among 23 PTIs, 6 were malignant (5 primary thyroid tumors and one metastasis from renal cell carcinoma), one was a follicular lesion of undetermined significance, and the rest were benign.

CONCLUSION

Despite being very rare, though probably underestimated, PTIs frequently signal the presence of unexpected lesions in the thyroid which differ from the indicated reason for which the patient was initially scanned and concerning which the risk of malignancy is not negligible.

PSMA expression by microvasculature of thyroid tumors - Potential implications for PSMA theranostics

Prostate-specific membrane antigen (PSMA) is overexpressed in prostate cancer epithelium, making it a promising target for molecular imaging and therapy. Recently, several studies found unexpected PSMA radiotracer uptake by thyroid tumors, including radioiodine-refractory (RAIR) cancers. PSMA expression was reported in tumor-associated endothelium of various malignancies, however it has not been systematically addressed in thyroid tumors. We found that PSMA was frequently expressed in microvessels of thyroid tumors (120/267), but not in benign thyroid tissue. PSMA expression in neovasculature was highly irregular ranging from 19% in benign tumors to over 50% in thyroid cancer. Such heterogeneity was not directly attributed to endothelial cell proliferation as confirmed by immunostaining with proliferation-associated endothelial marker CD105. PSMA expression was associated with tumor size (p = 0.02) and vascular invasion in follicular carcinoma (p = 0.03), but not with other baseline histological, and clinical parameters. Significant translational implication is that RAIR tumors and high-grade cancers maintain high level of PSMA expression, and can be targeted by PSMA ligand radiopharmaceuticals. Our study predicts several pitfalls potentially associated with PSMA imaging of the thyroid, such as low expression in oncocytic tumors, absence of organ specificity, and PSMA-positivity in dendritic cells of chronic thyroiditis, which is described for the first time.