Risk of Malignancy (ROM) in the various categories of the UK Royal College of Pathologists thy terminology for thyroid FNAC cytology: a systematic review and meta-analysis

Background - The UK Royal College of Pathologists Thy terminology for reporting thyroid FNAC cytology was first published in 2009, used throughout the United Kingdom and Ireland, in some parts of Italy and Switzerland, and elsewhere. There is no review of the literature or meta-analysis of the risk of malignancy (ROM) in the various categories of the UK Thy terminology. The study goal was to establish the published ROM for each Thy category and compare results with other existing terminology systems where similar meta-analyses were available.

Methods - A comprehensive literature search of online databases was conducted in May 2019 examining the ROM for histologically proven nodules with preoperative FNAC classified according to the UK Thy terminology.

Results - 25 articles were identified showing results of both cytology and histology. 12 of these were excluded to prevent selection bias as they showed data in just one Thy category. In the remaining 13 articles the pooled ROM was as follows; Thy 1: 12% (± 5-22%;95% CI); Thy 2: 5% (± 3-9%;95% CI); Thy 3: 22% (± 18-26%;95% CI); Thy 3a: 25% (± 20-31%;95% CI); Thy 3f: 31% (± 24-39%;95% CI); Thy 4: 79% (± 70-87%;95% CI); and Thy 5: 98% (± 97-99%; 95% CI) .

Conclusion - This meta-analysis shows comparable results to meta-analyses of other internationally recognised reporting terminologies for pooled risk of malignancy for surgically excised nodules in the various Thy reporting categories. There is comparatively little difference (6% only) between the pooled ROM of Thy 3a and Thy 3f surgically excised nodules.