Molecular imaging of advanced thyroid cancer: iodinated radiotracers and beyond

Role of PET/Computed Tomography in Elderly Thyroid Cancer: Tumor Biology and Clinical Management

PET/computed tomography (CT) studies can be potentially useful in elderly thyroid carcinoma patients for exploring the disease biology, especially in metastatic setting and thereby directing appropriate therapeutic management on case-to-case basis, adopting nuclear theranostics, and disease prognostication. With the availability of multiple PET radiopharmaceuticals, it would be worthwhile to evolve and optimally use FDG and the other non-fluorodeoxyglucose and investigational PET/CT tracers as per the clinical situation and need and thereby define their utilities in a given case scenario. In this regard, (I) differentiated thyroid carcinoma (DTC) including radioiodine refractory disease, poorly differentiated thyroid cancer (PDTC) and TENIS, (II) medullary thyroid carcinoma (MTC), (III) anaplastic carcinoma and (IV) Primary thyroid lymphoma (PTL) should be viewed and dealt separately.

Personalized Diagnosis in Differentiated Thyroid Cancers by Molecular and Functional Imaging Biomarkers: Present and Future

Personalized diagnosis can save unnecessary thyroid surgeries, in cases of indeterminate thyroid nodules, when clinicians tend to aggressively treat all these patients. Personalized diagnosis benefits from a combination of imagery and molecular biomarkers, as well as artificial intelligence algorithms, which are used more and more in our timeline. Functional imaging diagnosis such as SPECT, PET, or fused images (SPECT/CT, PET/CT, PET/MRI), is exploited at maximum in thyroid nodules, with a long history in the past and a bright future with many suitable radiotracers that could properly contribute to diagnosing malignancy in thyroid nodules. In this way, patients will be spared surgery complications, and apparently more expensive diagnostic workouts will financially compensate each patient and also the healthcare system. In this review we will summarize essential available diagnostic tools for malignant and benignant thyroid nodules, beginning with functional imaging, molecular analysis, and combinations of these two and other future strategies, including AI or NIS targeted gene therapy for thyroid carcinoma diagnosis and treatment as well.

PET/CT in the management of differentiated thyroid cancer

The standard treatment of differentiated thyroid cancer (DTC) consists of surgery followed by iodine-131 (¹³¹I) administration. Although the majority of DTC has a very good prognosis, more aggressive histologic subtypes convey a worse prognosis. Follow-up consists of periodically measurements of serum thyroglobulin, thyroglobulin antibodies and neck ultrasound and ¹²³I/¹³¹I whole-body scan. However, undifferentiated thyroid tumors have a lower avidity for radioiodine and the ability of DTC to concentrate ¹³¹I may be lost in metastatic disease. Positron emission tomography (PET)/computed tomography (CT) has been introduced in the evaluation of patients with thyroid tumors and the 2-[18F]-fluoro-2-deoxyd-glucose (¹⁸F-FDG) has been largely validated as marker of cell's metabolism. According to the 2015 American Thyroid Association guidelines, ¹⁸F-FDG PET/CT is recommended in the follow-up of high-risk patients with elevated serum thyroglobulin and negative ¹³¹I imaging, in the assessment of metastatic patients, for lesion detection and risk stratification and in predicting the response to therapy. It should be considered that well-differentiated iodine avid lesions could not concentrate ¹⁸F-FDG, and a reciprocal pattern of iodine and ¹⁸F-FDG uptake has been observed. Beyond ¹⁸F-FDG, other tracers are available for PET imaging of thyroid tumors, such as Iodine-124 (¹²⁴I), ¹⁸F-tetrafluoroborate and Gallium-68 prostate-specific membrane antigen. Moreover, the recent introduction of PET/MRI, offers now several opportunities in the field of patients with DTC. This review summarizes the evidences on the role of PET/CT in management of patients with DTC, focusing on potential applications and on elucidating some still debating points.

Thyroid cancer diagnosis in the era of precision imaging

Thyroid cancer affects 1.3% of the population with increasing rates of incidence over the last decade (approximately 2% per year). Although the overall prognosis is good in the differentiated subtypes, there has been a slow but steady increase in rate of deaths associated with thyroid cancer (approximately 0.7% per year over the last decade). Thyroid cancer is usually detected when: (I) patients feel a lump in the neck; (II) a routine clinical exam is performed; (III) an incidental thyroid nodule is identified on diagnostic imaging (e.g., CT neck or chest, carotid ultrasound, PET scan acquired for non-thyroid pathology). Identification of suspicious thyroid nodules results in further diagnostic work-up including laboratory assessment, further imaging, and biopsy. Accurate diagnosis is required for clinical staging and optimal patient treatment design. In this review, we aim to discuss utility of various imaging modalities and their role in thyroid cancer diagnosis and management. Additionally, we aim to highlight emerging diagnostic techniques that aim to improve diagnostic specificity and accuracy in thyroid cancer, thus paving way for precision medicine.

Targeting the pentose phosphate pathway increases reactive oxygen species and induces apoptosis in thyroid cancer cells

The pentose phosphate pathway (PPP) plays an important role in the biosynthesis of ribonucleotide precursor and NADPH. Cancer cells frequently increase the flux of glucose into the PPP to support the anabolic demands and regulate oxidative stress. Consistently, metabolomic analyses indicate an upregulation of the PPP in thyroid cancer. In the present study, we found that the combination of glucose-6-phosphate dehydrogenase (G6PD) and transketolase inhibitors (6-aminonicotinamide and oxythiamine) exerted an additive or synergistic effect on cell growth inhibition in thyroid cancer cells. Targeting PPP significantly increased cellular reactive oxygen species (ROS) and induced endoplasmic reticulum (ER) stress and apoptosis. Suppressed cell viability could be partially rescued with treatment with the ROS scavenger or apoptosis inhibitor but not ER-stress inhibitor. Taken together, dual PPP blockade leads to pharmacologic additivity or synergism and causes ROS-mediated apoptosis in thyroid cancer cells.

Thyroid cancer MR molecular imaging via SHP2-targeted nanoparticles

BACKGROUND

Molecular imaging has generated a great demand to develop targeted contrast agents for MR imaging.

MATERIALS AND METHODS

In this study, we synthesized Src homology 2-containing phosphotyrosine phosphatase 2 (SHP2)-targeted and polylactic-co-glycolic acid--based nanoparticles (NPs), which encapsulated perfluoropentane and being chelated with gadolinium (Gd3+) as an efficient molecular probe for targeting MR imaging on thyroid carcinoma.

RESULTS

These NPs displayed practical properties and favorable biocompatibility in vitro. Furthermore, they showed abilities to specifically target thyroid cancer and enhance MRI as a contrast agent in both in vitro and in vivo experiments.

CONCLUSION

This novel MR molecular imaging based on this SHP2-targeted contrast agent provides a useful and non-invasive method for the early detection of thyroid carcinoma.

Surveillance for Differentiated Thyroid Cancer Recurrence

Serum thyroglobulin monitoring along with anatomic and functional imaging play key roles in the surveillance of patients with differentiated thyroid cancer after initial treatment. Among patients with a disease stage justifying thyroid remnant ablation or with suspected metastatic disease, radioiodine whole-body scans are essential in the months after surgery. For patients with low to moderate-risk cancers, ultrasonography of the neck (with measurement of serum thyroglobulin on thyroid hormone replacement) are the best initial diagnostic modalities, and are often the only tests required. In individuals suspected of having distant metastases, CT, MRI, and 18F-FDG PET can make important contributions in localizing residual disease and monitoring its progression and responses to therapy, provided they are used in the appropriate setting.