Misrepresented multiple endocrine neoplasia 2: Do the British Thyroid Association guidelines accurately predict thyroid cancer risk in high-risk groups with multiple endocrine neoplasia 2? A case series.

Introduction: The incidence of thyroid nodules in the general population is around 40%. The British Thyroid Association U-grading has high sensitivity for identifying the common thyroid cancer subtypes (papillary and follicular). However, ultrasound features of the rarer medullary thyroid cancer differ, with lower sensitivity for ultrasound detection.Hereditary medullary thyroid cancer accounts for 25% of cases, forming part of the multiple endocrine neoplasia syndromes (multiple endocrine neoplasia 2) and is associated with RET proto-oncogene mutation, for which gene testing is increasingly available. This study aims to evaluate British Thyroid Association U-grading for thyroid cancer risk stratification in this high-risk population.

Case Report: This was a retrospective review of four multiple endocrine neoplasia 2 patients referred for thyroid ultrasound. A total of 10 thyroid nodules were graded as part of routine evaluation, taken from an endocrine and genetics tertiary referral centre. Patients with identifiable RET mutation from March 2017 to February 2023 were reviewed.

Discussion: Six patients had 10 thyroid nodules, of which 8 were graded as U2, 2 graded U3-5 and 8 confirmed as medullary thyroid cancer. However, two patients had no pathology data at the time of writing. For this cohort, U-grading and genetics were discordant, with RET gene testing more effective than ultrasound in cancer detection. All nodules should be considered high risk for medullary thyroid cancer, regardless of U-grade.

Conclusion: Our data demonstrate that British Thyroid Association U-score has limited value for medullary thyroid cancer detection in this high-risk group and cannot be used for risk stratification or surveillance. As a rarer thyroid cancer subtype, medullary thyroid cancer and the high-risk multiple endocrine neoplasia 2 population are under-represented in British Thyroid Association 2014 guidance and deserve consideration in future editions.