Screening may not be accurate word to represent the cases submitted to PET/CT evaluation for primary tumor in a patient who has abnormal serum tumor marker.

OBJECTIVE: Determine the value of PET/CT in unknown primary cancer patient with high tumor marker and negative study for clinical and conventional imaging. MATERIAL AND METHOD: A retrospective database review of 417 patients who received PET/CT between July 2006 and August 2007 in National cyclotron and PET center at Chulabhorn cancer center was done. Patients were included in this study if the diagnosis were unknown primary cancer and rising tumor marker. Twelve patients were included in this study. Data included age, gender, tumor marker rising, anatomical imaging finding (CT and MRI), PET finding and clinical follow-up. RESULTS: Nine cases had normal PET/CT. This showed that PET/CT does not get more information than conventional imaging. The PET scan showed positive in three cases, #5, #6 and #10. Two cases were false positive, #5 and #6. Case #5 had clinical follow-up for one year and revealed to be normal. Case #6 PET showed markedly glucose avid lesion at tumor thrombus but contrast CT confirm blood clot and the patient was treat with wafarin and claxane. The follow-up clinical showed improvement. The high serum CA 125 explained by lung infarction caused the false positive. In case #10, the PET/CT suggested lung cancer at basal segment of LLL. CONCLUSION: Screening 18F FDG PET/CT is not appropriate in unknown primary with rising tumor marker and normal conventional imaging is required.