Evaluation of Positron-emission Tomography in the Diagnosis of Primary Tumours in Patients Presenting with Metastases: Prospective Study

TK Au Yong, CP Wong, YK Leung, KS Chu, WCM Tong

Hong Kong J Radiol 2005;8:9-14

Objective: To study the value of positron-emission tomography using 2-fluoro-2-deoxy-Dglucose labelled with fluorine 18 in locating unknown primary tumour sites in patients presenting with metastases.

Patients and Methods: Between November 2003 and December 2004, a total of 62 consecutive patients were referred to the Queen Elizabeth Hospital for positron-emission tomography after receiving a presumptive diagnosis of metastasis with an unknown primary tumour. Positron-emission tomography was performed from the thigh to the head, and results were compared with the final diagnostic (either histological or clinical) findings.

Results: Of the 62 patients studied, positron-emission tomography detected 36 (58%) suspected primary lesions, of which 3 were false positives. For 11 patients, the suspected metastases were later found to be non-metastatic (either primary brain tumours or nonmalignant lesions); hence, the detection rate of primary tumour sites by positronemission tomography was 71% (36/51). Brain metastasis was the most common reason for referral (n = 25); positron-emission tomography had 100% sensitivity, 90% specificity, and 96% accuracy for diagnosing extracranial primary tumours. Cervical lymph node metastasis was the second most common reason for referral (n = 13); positron-emission tomography detected 62% of primary sites in this patient subgroup.

Conclusion: Positron-emission tomography using 2-fluoro-2-deoxy-D-glucose labelled with fluorine 18 is a valuable diagnostic tool that can locate primary tumour sites in patients presenting with metastases.