It is difficult to imagine the time in medical history when “medical imaging” was limited to simply seeing the patient in person. Since then, an arsenal of medical imaging tools has become available, and medical students are taught how to use them from the very start of their education, as if these tools have always been a part of medical practice.
Some of the medical imaging modalities we have are rather more “primitive” (for lack of a better word) than others, such as ultrasound scans. MRIs, CT scans, and colonoscopies provide a much better view of what’s going on inside the body, but they are more expensive and usually entail a waiting time.
Today, medical imaging has become an indispensable part of medicine. It has reached a point in which its wilful exclusion can be litigated. Whole protocols are now designed around medical imaging. This is certainly true for neuroendocrine tumors such as medullary thyroid carcinoma (MTC).
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Read more about MTC etiology
Yordanova et al concur on the indispensable role of medical imaging today, writing, “In modern oncology, imaging is necessary for treatment planning, tumor staging and follow-up.” This is because the wealth of information that it yields is simply too valuable to be ignored; treating a patient with a neuroendocrine tumor without medical imaging today would be downright unthinkable.
Yordonova and colleagues also wrote, “Molecular imaging with positron emission tomography (PET) or single photon emission computed tomography (SPECT) enables real-time visualization of tumor receptors, metabolism and pathogenesis.” The emphasis here is on “real-time”; this technically allows physicians to stay one step ahead in tracking the progression of the disease.
Let’s continue to explore what medical imaging for neuroendocrine tumors can do.
A New Way Of Seeing
Refardt et al, in their study on medical imaging for neuroendocrine neoplasms, wrote, “Accurate and informative imaging is crucial for correct diagnosis, staging, and treatment decision.” Diagnosis, staging, and treatment—that pretty much covers every step of the clinical decision-making process.
One of the most important imaging modalities for the evaluation of neuroendocrine tumors is CT imaging. CT scan machines are widely available (most hospitals are equipped with them) and scans can be carried out speedily once the patient’s turn has arrived.
Refardt and his team covered the uses of CT scans for various forms of neuroendocrine neoplasms, including pancreatic, liver, colonic, and rectal neoplasms. The most common sites of neuroendocrine tumors are the lungs and the gastrointestinal tract.
On MTC specifically, they wrote, “For thoracic neuroendocrine neoplasms, IV contrast-enhanced chest CT is the morphological imaging technique of choice. Thin section CT chest scanning is useful to establish localization and metastatic spread.” MRI scans, on the other hand, are superior for soft tissue characterization.
Read more about MTC diagnosis
A relatively new imaging modality that has gained increasing attention is somatostatin receptor imaging. To understand how it works, we first need to recognize that somatostatin receptors (SSTRs) can be found on the surface of most well-differentiated neuroendocrine neoplasms (SSTR expression density is decreased in poorly differentiated neuroendocrine neoplasms).
Because of this, Refardt and colleagues wrote, “Evaluating the SSTR expression in a neuroendocrine neoplasm patient improves tumor localization and staging, but also opens new treatment options with peptide receptor radionuclide therapy (PRRT) in patients with sufficient expression.”
Youdonova et al, in their study on SSTR imaging, discussed protocols for SSTR-positive and SSTR-negative neuroendocrine tumors. Like Refardt et al, they agreed that “SSTR imaging was shown not only to correlate with the gene expression of SSTR in neuroendocrine tumors,” but that “the molecular imaging of neuroendocrine tumors has a major impact on treatment planning.”
With regards to SSTR-negative neuroendocrine tumors, the management becomes more challenging. There are multiple potential targets for the molecular imaging and treatment of SSTR-negative neuroendocrine tumors, including, for example, glucose transporter-1, fibroblast activation protein, and glucagon-like peptide-1 receptor.
However, there is much room for improvement in the field of SSTR-negative tumor imaging; as Yordonova and colleagues wrote, “The development of better diagnostic and therapeutic modalities [for SSTR-negative neuroendocrine tumors] is increasingly important.”
Future Directions
The future of medical imaging for neuroendocrine tumors such as MTC lies in better imaging modalities that can go further in helping us visualize in real-time what goes on inside tumors, and how treatment is making a difference. We can take comfort in the fact that scientists are exploring every possible imaging modality to aid in the diagnosis and treatment of neuroendocrine tumors, and indeed, many other diseases as well.
Refardt and colleagues ended their paper with an intriguing suggestion that artificial intelligence may yet play a vital role in the future of visualizing neuroendocrine tumors.
They wrote about an area of study called radiomics: “Radiomics, defined as the use of advanced computer analysis and deep learning techniques to find and quantify imaging, have the potential to lead to more differentiated grading, even allowing prediction of treatment response.”
This technique has been used to differentiate between low-grade and high-grade tumors, and has even been trialed as a prognostic tool. If scientists can turn this novel tool into something suitable for everyday clinical use, it could potentially be a game-changer in the treatment of neuroendocrine neoplasms such as MTC.
References
Refardt J, Hofland J, Wild D, et al. New directions in imaging neuroendocrine neoplasms. Curr Oncol Rep. Published online November 4, 2021. doi:10.1007/s11912-021-01139-2
Yordanova A, Biersack H-J, Ahmadzadehfar H. Advances in molecular imaging and radionuclide therapy of neuroendocrine tumors. J Clin Med. 2020;9(11):3679. doi:10.3390/jcm9113679
