Clinical Outcomes of Follicular Thyroid Carcinoma Did Not Significantly Differ according to Tumor Size in an...

Follicular thyroid carcinoma (FTC) measuring <2 cm is generally associated with good prognosis, while tumor size ≥4 cm is regarded as being associated with a poor prognosis. This study aimed to evaluate FTC prognosis by tumor size to investigate whether the 2- and 4-cm criteria are appropriate for assessing prognosis.

Data of 248 patients with FTC diagnosed between August 1995 and June 2021 were retrospectively analyzed. The population was divided into four groups according to tumor size: <2.0, 2.0-3.9, 4.0-5.9, and ≥6.0 cm. Distant metastasis (DM), recurrence and/or structural persistence (R/SP), cancer-specific death (CSD), and frequency of telomerase reverse transcriptase (TERT) promoter mutations based on tumor size were evaluated.

While the rates of DM, R/SP, and CSD and the frequency of TERT promoter mutations did not differ among the size groups <6 cm, they increase sharply in tumor size ≥6 cm, although statistically insignificant (P=0.608, P=0.248, P=0.089, and P=0.165 respectively). Widely invasive subtypes, and TERT promoter mutations were significantly associated with DM (P=0.009 and P<0.001, respectively). Age ≥55 years, gross extrathyroidal extension, synchronous DM, and TERT promoter mutation were independent risk factors for CSD (P=0.005, P=0.003, P<0.001, and P=0.002, respectively).

DM, R/SP, CSD, and TERT promoter mutations were not uncommon in FTCs <2 cm compared to those in larger FTCs, whereas FTCs ≥6 cm showed a sharp decline in prognosis, although this was statistically insignificant.