Natural History and Predictive Factors of Outcome in Medullary Thyroid Microcarcinoma

Abstract

Purpose Management of sporadic medullary thyroid microcarcinoma smaller than 1 cm (micro-MTC) is controversial due to conflicting reports of prognosis. As these cancers are often diagnosed incidentally, they pose a management challenge when deciding on further treatment and follow-up. Methods Micro-MTCs were identified from a prospectively maintained surgery database and slides were reviewed to determine pathological grade. The primary endpoints were recurrence, time to recurrence and disease-specific survival. 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. The included patients had a median age of 60, tumour size of 4 mm, and 28 (67%) were female. The diagnosis was incidental in 36 (86%) with 4 (10%) being high-grade, 5 (12%) having LNM and 9 (21%) having elevated post-operative calcitonin. Over a 6.6-year median follow up, 5 (12%) developed recurrence and 3 (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, LNM and raised calcitonin were associated with recurrence (P < 0.01). Tumour size and type of surgery were not significantly associated 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 generally associated with good outcomes. Size is not significantly associated with outcomes. Utilising grade, LNM and post-operative calcitonin allows for identification of patients at risk of recurrence to personalise management.

Clinicopathological characteristics and prognosis of medullary thyroid microcarcinoma: a tumor with a similar prognosis to macrocarcinoma

“…Machens et al [ 21 ] studied 233 patients with MTMC and found that lymph node metastases were common. In a recent study, Kesby et al [ 22 ] studied 42 patients with MTMC, of which five (12%) had lymph node metastases; during a median follow-up of 6.6 years, five (12%) had recurrence, and three (7%) died. In summary, studies of MTMC have led to very different conclusions from those of papillary thyroid microcarcinoma.…”