Criteria for follow-up of thyroid nodules diagnosed as follicular neoplasm without molecular testing - The experience of a high-volume thyroid centre in Japan

Background Clinical management of follicular neoplasms (FNs) using molecular testing of thyroid-aspirated materials is not routinely performed in Japan. This article aims to identify low-risk FN nodules that can be followed up without molecular testing. Methods The relationship between preoperative findings, factors influencing surgical decision, and the risk of malignancy (ROM) was examined in 356 thyroid nodules with cytological diagnosis of FN at Kuma Hospital from January to December 2020. Results ROMs of FN with cytology results favouring malignancy (41.2%) were significantly higher than those favouring benign (7.7%) or borderline (8.2%) (p < .001). Moreover, ROMs of FN with ultrasonography results of high suspicion (54.5%) were significantly higher than those with low (4.5%) or intermediate suspicion (0%) (p < .0001). There was a large difference in overall ROM in tumours bordering 30 mm in size (<30 mm; 3.6%, >= 30 mm; 20.0%). ROMs of FNs with a tumour volume doubling rate (TVDR) of 1.0/year or more (28.6%) were higher than those of FNs with a lower TVDR (9.9%) (p < .05). The ROMs of FNs with or without one or more of the following four findings suggestive of malignancy: cytological findings favouring malignancy, ultrasonography findings of high suspicion, tumour size >= 30 mm, and TV-DR >= 1.0/year, were 14.6% and 1.0%, respectively. Conclusion FNs with no cytological findings favouring malignancy, no ultrasonography findings of high suspicion, tumour size <30 mm and TV-DR <1.0/year, are considered low risk and can be followed up without the need for molecular testing.