18F-FDG PET/CT can aid the noninvasive preoperative determination of malignancy and may be helpful in detecting metastases of malignant cardiac tumors, according to a small study published in the June issue of the Journal of Nuclear Medicine.
Primary cardiac tumors are rare, with an incidence ranging from 0.001 to 0.028 percent in autopsy reports, according to the study authors. Approximately 20 to 25 percent of these tumors are malignant, with angiosarcoma being the most common malignant cardiac tumor. In contrast, secondary cardiac tumors, such as metastasis to the heart from other malignant tumors, occur more frequently.
In the diagnostic algorithm of cardiac tumors, the noninvasive determination of malignancy and metastatic spread is of major interest to stratify patients and to select and monitor therapies, wrote Kambiz Rahbar, of the nuclear medicine department at University Hospital Münster in Münster, Germany, and colleagues. In the diagnostic work-up, morphologic imaging modalities such as echocardiography or MRI offer information about size, invasiveness and vascularization. However, preoperative assessment of malignancy may be unsatisfactory.
Thus, the researchers sought to evaluate the diagnostic value of 18F-FDG PET and the incremental diagnostic value of an optimized CT score in this clinical scenario. They noted that this modality has not yet been systematically evaluated for the characterization of cardiac tumors.
For the study, the investigators analyzed 18F-FDG PET/CT scans (whole-body imaging with low-dose CT) of 24 consecutive patients with newly diagnosed cardiac tumors (11 men, 13 women; mean age, 59 years). They measured the maximum standardized uptake values (SUVmax) of the tumors, and divided the patients into two groups: benign cardiac tumors (seven) and malignant cardiac tumors (17: cardiac primaries [eight] and metastases [nine]). Then, they compared the SUVmax between the two groups, and compared the results with contrast-enhanced CT, using standardized criteria of malignancy.
Mean SUVmax was 2.8 in benign cardiac tumors and significantly higher both in malignant primary and in secondary cardiac tumors (8 and 10.8), the researchers wrote. Malignancy was determined with a sensitivity of 100 percent and specificity of 86 percent (accuracy, 96 percent), after a cutoff with high sensitivity (SUVmax of 3.5) was chosen to avoid false-negatives. Morphologic imaging reached a sensitivity of 82 percent and a specificity of 86 percent (accuracy, 83 percent).
Rahbar and colleagues also reported that both false-positive and false-negative decisions in morphology could be corrected in all but one case using a metabolic threshold with an SUVmax of 3.5. In addition, extracardiac tumor manifestations were detected in four patients by whole-body 18F-FDG PET/CT.
While the authors acknowledged that the study’s retrospective nature is its “main limitation,” they concluded that their findings show that “quantification of 18F-FDG uptake can support the noninvasive, pretreatment differentiation between benign and malignant cardiac tumors… With a cutoff SUVmax of 3.5, 18F-FDG PET could be used to noninvasively determine tumor malignancies with a sensitivity of 100 percent in our series. Only one benign tumor was misdiagnosed (specificity, 86 percent).” They added that larger studies should further define the optimal cutoff. In fact, Rahbar et al recommended that future prospective studies in larger patient groups are “desirable to establish an optimal imaging pathway before therapy.”