Value of (99m)Tc tetrofosmin scan in well-differentiated thyroid cancer.

Background: Patients with cold thyroid nodules without ultrasound malignant suspicion and with benign/undetermined cytology may be subjected to follow-up surveillance. 99mTc-tetrofosmin scan (99mTc-TS) may identify patients where this observation can be performed with more certainty. Absence of uptake never occurs in carcinoma patients. Our objective was to determine the 99mTc-TS negative predictive value (NPV) in patients with cold thyroid nodules.

Methods: An evaluation with 99mTc-TS was conducted prior to surgery in patients with thyroid gland tumor who were candidates for surgery. All patients underwent thyroidectomy according to histology; NPV and test sensitivity were evaluated when compared with the histopathological result. Then, 296-370 MBq (8-10 mCi) of 99mTc-tetrofosmin was administered, and scan images were evaluated after 120 min. Scan result was reported as a) with increased metabolic activity (IMA) or b) without increased metabolic activity (WIMA).

Results: Included in the study were 86 consecutive patients. In 60 patients the scan showed IMA, 20/60 (33%) with carcinoma, 67% with benign nodule. In 26 (30.2%) the scan was WIMA. In this group, 3/26 (11.5%) had carcinoma and (88.4%) had a benign neoplasia. Sensitivity = 91.43 (95% CI = 80.73-100), specificity = 45.10 (95% CI = 30.46-59.73), positive predictive value = 53.33 (95% CI = 39.8-66.79) and NPV = 88.46 (95% CI 74.26-100). Negative probability ratio = 0.19.

Conclusions: IMA-99mTc-TS is less specific in thyroid cancer; nevertheless, in WIMA patients the possibility of carcinoma is 13%. Most patients (70%) showed IMA, 33% with carcinoma. WIMA-NPV = 30%. 99mTc-TS may be useful in the therapeutic decision of patients with thyroid nodule with concerns about surgery. Its usefulness lies in the NPV.