The uptake of the radiopharmaceutical fluoro methyl tyrosine (FMT) on PET imaging in patients with pulmonary adenocarcinoma is a significant independent predictor of poor prognosis, according to research published in this month’s issue of the Journal of Nuclear Medicine.
“We found that FMT uptake correlated with the expression of L-type amino acid transporter 1 (LAT1) and that both LAT1 expression and FMT uptake were significantly higher in non-adenocarcinomatous disease than in adenocarcinoma,” wrote the authors of the study.
The researchers, from the department of medicine and molecular science at the Gunma University Graduate School of Medicine in Gunma, Japan, noted that LAT1 is over expressed in malignant tumors and is associated with tumor proliferation, angiogenesis and poor survival.
FMT is an amino-acid tracer developed at the facility for PET imaging. The authors conducted a study on 106 consecutive non-small cell lung cancer (NSCLC) patients at the facility to compare the prognostic significance of FMT with the standard PET radiotracer, FDG.
FMT PET was performed as part of the staging work-up. The patients also underwent FDG PET, CT of the thorax, whole-body bone scanning for the detection of possible distant metastases and bronchoscopy with biopsy for diagnostic confirmation. The mean interval between the PET studies, performed on a Shimadzu SET 2400W system, was six days, according to the authors.
The FDG and FMT images were interpreted by two nuclear medicine physicians in consensus. Semiquantitative analysis was performed using attenuation-corrected transaxial images, radiotracer dosage, patient body weight and cross-calibration between PET and a dose calibrator in order to derive a standardized uptake value (SUV).
Survival was recorded from histologic diagnosis to death or the last follow-up, the authors stated. The median survival time in the patient cohort was 26 months and the two-year overall survival rate was 54.4 percent. They found that the two-year overall survival rate of patients with a low SUV (below 1.6) and those with a high SUV (greater than 1.6) on FMT PET were 75 percent and 46.7 percent, respectively.
The two-year overall survival rates of the patients with a low SUV (less than 11) and high SUV (greater than 11) on FDG PET were 67.2 percent and 40.9 percent, respectively.
“The adenocarcinoma patients with a high SUVmax on both PET studies demonstrated a significantly poor prognosis, compared with those with a low SUVmax,” the authors wrote. “In the patients without adenocarcinoma, however, no significant difference was observed between high SUVmax and low SUVmax group on either PET study.”
On the basis of their findings, the researchers found that an FMT uptake with a SUV cutoff of 1.6 for the primary tumor was a significant independent factor in predicting a poor prognosis in patients with adenocarcinoma.
“These results indicate that, compared with FDG PET, FMT PET seems to be the stronger prognostic factor in patients with NSCLC, especially adenocarcinoma,” the authors wrote. “In patients without adenocarcinoma, FMT uptake in the primary tumor did not have a significant relationship with survival.”