1. McGraw, Mark

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According to new research, brain PET imaging with carbon-11 methionine (C-11 MET) has potential to be useful for diagnosing developmental brain tumors in children and adolescents. Published in PLOS One, the study evaluated imaging findings in patients with intracranial germinomas (IGs) who underwent C-11 MET PET/CT scans (2022;

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Led by Seung Hwan Moon, MD, an instructor in the Department of Nuclear Medicine at Samsung Medical Center, Seoul, Republic of Korea, a team of researchers compared the results with standard clinical lab variables for diagnosing the tumors, finding that C-11 MET performed as well as clinical lab variables and could be useful as a means of helping clinicians find tumors before they could start to spread.


IGs originate from totipotent germ cells, which usually occur in children and young adults, and are the most common type of intracranial germ cell tumors, the researchers noted, adding that these tumors account for as much as 2.1 percent of all pediatric primary brain tumors.


"IGs are potentially malignant in behavior and can infiltrate normal brain tissue, as well as spread through the whole of the central nervous system," the study authors wrote, adding that "these lesions are highly sensitive to radiotherapy and/or chemotherapy, and are potentially curable without complete surgical resections."


And, given that these tumors have what the researchers described as "a highly favorable treatment response," and delaying treatment can cause more severe neurologic complications, early and accurate diagnosis "is essential for better clinical outcomes in patients with IGs."


"Clinical diagnosis and staging of IGs are based on symptoms, tumor markers such as [alpha]-fetoprotein (AFP) or [beta]-human chorionic gonadotropin (HCG) in serum and cerebrospinal fluid, and brain and spinal MRI. AFP or HCG values beyond a certain threshold in either the serum or cerebrospinal fluid suggest the presence of these specific tumors," the authors wrote.


"However, on the basis of experience from previous clinical studies, the defined thresholds can vary according to clinical scenario," they continued. "MRI is more sensitive than computed tomography and thus is considered the imaging modality of choice. However, in some cases of basal ganglia germinomas, it was difficult to detect the tumor lesions because the lesions in basal ganglia only show subtle signal change, no mass effects, and nonspecific radiological findings on MRI during their early stages. Therefore, an additional biomarker reflecting the tumor characteristics would improve diagnosis and management of these tumors."


With all of these factors in mind, the purpose of the research was to "investigate the value of C-11 methionine positron emission tomography/computed tomography in patients with intracranial germinoma," wrote the authors, who conducted a retrospective study of 21 consecutive patients with pathologically confirmed IGs and eight patients with intracranial non-germinomas (INGs) located in a similar region.


The researchers used clinical characteristics, imaging findings, and tumor markers such as AFP and HCG as clinical variables. Maximum standardized uptake value (SUVmax), tumor-to-normal tissue (T/N) ratio, and visual scoring of tumor were used as MET-PET parameters.


According to the research, "overall, all IGs were well-visualized on MET-PET with a three-grade visual scoring system. In addition, SUVmax of IGs was higher than that of INGs (P=0.005). Pre-treatment (Pre-Tx) T/N ratio was significantly correlated with pre-Tx serum HCG (P=0.031). Moreover, MET-PET parameters showed significant associations with tumor location, sex, KRAS variant, and symptoms."


Ultimately, MET PET/CT could be a useful diagnostic tool in patients suspected of having IGs," the researchers concluded. "In addition, the MET avidity of tumor is a potential surrogate biomarker of HCG, which has been used as a diagnostic marker for IGs. Tumor MET parameters also had significant differences according to tumor locations, sex, symptoms, and KRAS mutation. However, MET avidity of tumors had no significant prognostic value."


Mark McGraw is a contributing writer.