A PET Tracer May Improve Diagnosis of Medullary Thyroid Carcinoma

A new study showed promising results for the use of the β-amyloid-specific radiotracer [¹⁸F]AV-45 in medullary thyroid carcinoma (MTC) diagnosis with positron emission tomography (PET)/computed tomography (CT) imaging.

“In this first-in-human pilot clinical study, we have demonstrated that [¹⁸F]AV-45 exhibits selective and specific uptake by the amyloid plaques in MTC tissue samples,” the study authors stated.

They observed localized accumulation of [¹⁸F]AV-45 in tumor tissue sections from 5 patients diagnosed with MTC, with a similar distribution pattern in the amyloid plaques as that found with hematoxylin and eosin (H&E) and Congo Red stainings.

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In contrast, the analysis of healthy human thyroid tissue showed minimal uptake of the radiotracer, which suggested a selective and specific accumulation of [¹⁸F]AV-45 in MTC amyloid plaques.

Moreover, [¹⁸F]AV-45 performed better than 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) in the identification of lymph node metastasis in a recurrent MTC patient. PET imaging studies showed several neck lymph nodes with increased [¹⁸F]FDG uptake but only one with increased [¹⁸F]AV-45 uptake. Postoperative analysis confirmed that only the [18F]AV-45-positive lymph node corresponded to an MTC metastasis with amyloid plaque deposition.

These results for [¹⁸F]FDG are in accordance with previous studies, which reported false-positive diagnoses of lymph node metastasis due to local inflammation. In contrast, [¹⁸F]AV-45 seems to specifically detect MTC lymph node metastasis.

The [¹⁸F]AV-45 radiotracer has been suggested as a promising contrast reagent to detect amyloid deposition in other tissues. In MTC, amyloid deposition is mainly formed by misfolded calcitonin, which has β-sheets in its secondary structure. Therefore, the use of a specific molecular probe for β-amyloid such as [¹⁸F]AV-45 to recognize amyloid deposition, an important feature in MTC, might improve diagnostic imaging.

Reference

Li C, Zhang P, Nie R, et al. Targeting amyloids with [¹⁸F]AV-45 for medullary thyroid carcinoma positron emission tomography/computed tomography imaging: a pilot clinical study. Mol Pharm. Published online January 4, 2022. doi:10.1021/acs.molpharmaceut.1c00680