Purpose: The aim of this study was evaluate biochemical incomplete response (BIR) in Middle Eastern differentiated thyroid cancer (DTC), identify factors that could predict BIR before radioactive iodine (RAI) ablation and to investigate the long-term clinical outcome of DTC patient exhibiting BIR to initial therapy.

Methods: We retrospectively evaluated 1286 DTCs from Middle Eastern ethnicity who underwent total thyroidectomy and RAI therapy. Demograpic and clinico-pathological factors predicting BIR were evaluated. The outcome of these patients was analyzed using primary outcome of structural disease and disease-free survival (DFS).

Results: With a median follow-up of 10 years, 266 (20.7%) patients had BIR. High pre-ablation stimulated thyroglobulin (presTg), presence of lymph node metastasis, male gender and delayed initial RAI therapy (≥3 months) after thyroidectomy were significant independent predictors of BIR. Upon evaluating long-term clinical outcomes in 266 patients with BIR, we found 36.8% of patients developed structural disease. Male sex (OR = 1.56; 95% CI = 1.05-2.30; p = 0.0272) and increasing Tg after initial therapy (OR = 4.25; 95% CI = 1.93-10.82; p = 0.0001) were independent risk factors for structural disease in patients with BIR. DFS was significantly worse if both these risk factors existed concomitantly (p < 0.0001).

Conclusion: To achieve the fair efficacy of RAI therapy, early prediction of BIR before RAI ablation is desirable. Our finding of the clinico-pathological factors (high presTg level, LNM, delayed RAI therapy and male gender) could serve as easy and robust early predictors of BIR. In addition, DTC patients exhibiting BIR had a high risk of structural disease and hence personalized management approach would be preferable for BIR patients to ensure best clinical outcome.