Endocrine Abstracts

The work-up of Differentiated Thyroid Cancer (DTC) patients includes thyroid surgery, thyroid remnant ablation (TRA) with 131-radioiodine and long life follow-up. 131I-post therapy whole body scan (pT-WBS) and thyroglobulin (Tg) are used in identifying metastatic patients. Some authors suggested to use post-surgical Tg (ps-Tg) values in deciding for or against TRA. The aim of our study was to verify the sensitivity and PPV of 131I-pT-WBS compared to serum Tg levels in detecting metastases in early stage of DTC patients.

Material and method: We retrospectively reviewed the records of 570 patients affected by pT1-pT3 DTC (F=450, M=120, mean age 48.5±13.2; F/M ratio=3.7:1) referred to our Nuclear Medicine Unit in the last five years. None of our patients had: 1) loco-regional or distant metastases at the time of recruitment; 2) age ≤16 years; 3) positive thyroglobulin-antibody (Tg-Ab); 4) pT₄ stage, 5) poorly-differentiated thyroid cancer. The majority of patients (98.2%) were affected by papillary carcinoma. Before TRA, all patients underwent neck-ultrasonography, laboratory test and, if treated in hypothyroid state (321/570, 56%), radioiodine thyroid uptake. Both ps-Tg and Tg values obtained at TRA were matched with 131I pT-WBS results.

Results: 131I pT-WBS discovered metastases in 82 out of 570 (14.4%) patients. Seventy-three out of these patients (90.2%) showed ps-Tg levels ≤1 ng/ml. At TRA, forty of them (54%) maintained Tg levels ≤1 ng/ml. The majority of these patients (38/40, 95%) showed lymph-node metastases at 131I-pT-WBS while three had lung metastases (one of them showed lymph-node metastasis). The metastases were confirmed by targeted morphological studies.

Conclusion: ps-Tg cannot be used to decide for or against TRA. In early stage of DTC, 131I-pT-WBS is an accurate method in detecting metastases also in patients with stimulate Tg values ≤1 ng/ml, showing sensitivity and PPV significantly higher than Tg (100% vs 29.3% for both).