Patterns of metastasis in follicular thyroid carcinoma and the difference between early and delayed presentation

Introduction Follicular thyroid cancer (FTC) has a good prognosis if treated early. The aim of this study was to look at the difference in outcomes in those who presented with metastasis early or late in their disease. Methods A retrospective cohort study was conducted of patients diagnosed with FTC (n=91) treated between 2000 and 2013. Demographic, laboratory, pathological and survival data were collected and analysed. Results Metastatic FTC was diagnosed in 20 cases (22%). The median age at diagnosis was 65 years (range: 17-86 years) and 65% of the patients were female. Twelve patients (60%) were diagnosed with metastatic disease at presentation, with the bones being the most common site (75%). In the remaining eight cases (40%), metastasis developed at a median of 4.5 years (range: 2-8 years) after initial thyroid surgery, lungs being the most common site (50%). Eighteen patients (90%) underwent surgical intervention for the primary disease. Sixteen patients (80%) received adjuvant radioactive iodine and eight (40%) received external beam radiotherapy. Widely invasive follicular cancer was the predominant histological diagnosis (90%). No prognostic association was observed with any of the parameters studied. The overall disease specific mortality rate was 40%. There was no significant difference in mortality between those who presented with metastatic disease and those who developed metastasis during the follow-up period (33% vs 50%, p=0.61). Conclusions The clinical outcome and prognosis for cases with metastatic disease is generally poor. Despite this, almost half of the patients in our study were still alive at a median follow-up of 5.5 years, regardless of whether they were diagnosed with metastatic disease on initial presentation or whether they developed metastasis after initial thyroid surgery.