Balancing treatment of sporadic Medullary Thyroid Microcarcinoma

Abstract

Background: Management of sporadic medullary thyroid microcarcinoma smaller than 1cm (micro-MTC) is controversial due to conflicting reports of prognosis and due to many series including both hereditary and sporadic patients. As these cancers are often diagnosed incidentally, they pose a significant management challenge. Methods: Micro-MTCs were identified from a prospectively maintained surgery database and were reviewed to determine the international medullary thyroid carcinoma grading system (IMTCGS) grade. The primary endpoints were time to recurrence and disease specific survival (DSS). Prognostic factors assessed included size, grade, lymph node metastasis (LNM) and post-operative calcitonin. Results: From 1995-2022, 64 patients were diagnosed with micro-MTC with 22 excluded due to hereditary disease, 67% were female with a median age of 60 and a median tumour size of 4mm. The diagnosis was incidental in 86% with 10% being high grade, 12% having LNM and 21% had elevated post-operative calcitonin. Over a 6.6-year median follow up, 12% developed recurrence and 7% died from MTC. High grade and LNM was associated with 10-year survival estimates of 75% versus 100% for low grade and no LNM (HR=831, P<0.01). High grade, lymph node involvement and raised calcitonin were associated with recurrence (P<0.01). Tumour size and surgical approach did not have any significant association with recurrence or survival. No patients with low grade micro-MTC and normal post-operative calcitonin developed recurrence. Conclusions: Most sporadic micro-MTC are detected incidentally and are associated with good outcomes, but a small number develop recurrence. Size is not significantly associated with outcomes. Utilising grade and post-operative calcitonin allows for identification of patients at risk of recurrence to personalise management.