Prognostic implications of diffuse hepatic uptake following I-131 therapy for differentiated thyroid cancer.

Objectives Radioactive iodine (I-131) therapy (RIT) is an effective method of treatment for relapse or metastasis after DTC surgery, and RIT significantly improves the prognosis of recurrent DTC. Post I-131 whole body scan (WBS) frequently reveals diffuse uptake in the liver. This suggests the presence of organic iodine and has been considered a sign of treatment benefit by some physicians. However, the criteria used to determine the presence of hepatic uptake often depend on the physicians’ personal experience; therefore, the results are variable. This study aimed to investigate whether quantitative evaluation of hepatic uptake on I-131 WBS has association with prognosis of DTC patients.

Methods This is a retrospective study of patients treated for DTC at our hospital between April 2004 and June 2014. All patients included in the study had no uptake of remnant or other lesion with I-131 WBS. A total of 185 patients met these criteria. I-131 WBSs were then quantified on hepatic uptake ratio (H/B). H/B was defined as follows: (hepatic uptake) / (background uptake). The progression-free survival (PFS) after RIT was analyzed by Kaplan-Meier method using several H/B cutoff points and log-rank analysis.

Results PFS were 74.3%, 74.1%, 71.7%, 65.8%, 51.7% and 5.3% for H/B cutoff points 1.0, 1.1, 1.2, 1.3 1.4 and over 1.5, respectively, at 5 years (figure). The patients with H/B>1.5 had poorer prognosis than those with H/B>1.4 (P<0.00001).

Conclusions DTC patients with higher hepatic uptake (H/B>1.5) are less likely to become progression-free after RIT than those with lower uptake. Increased hepatic uptake could suggest the presence of occult disease.