Procalcitonin in Medullary Thyroid Carcinoma: An Umbrella Review of Systematic Reviews and Meta-Analyses

Background/Objectives: Procalcitonin has been proposed as an alternative or complementary biomarker to calcitonin in medullary thyroid carcinoma (MTC). We synthesised the published systematic reviews, appraised their quality, and measured their reliance on the same primary studies. Methods: Umbrella review of systematic reviews reporting measured procalcitonin values in proven or suspected MTC. PubMed/MEDLINE and the Cochrane Library were searched to 30 June 2026. Quality was appraised with AMSTAR-2 and overlap as the corrected covered area (CCA). Results: Seven evidence syntheses (2015–2024) were included, four addressing procalcitonin itself and two with meta-analysis. Across diagnostic and monitoring populations, a bivariate meta-analysis of 11 studies and 5817 patients gave sensitivity of 0.90 (95% CI 0.71–0.97) and specificity of 1.00 (95% CI 0.85–1.00); in postoperative surveillance, five studies and 296 patients gave pooled sensitivity and specificity of 96%. The five syntheses enumerating their sources drew on 21 distinct primary reports, giving a corrected covered area of 38.1%, every pairwise value above the 15% threshold for very high overlap. Two primary studies were extracted discordantly; for one of them the same data yielded specificities of 84% and 5% depending on the threshold and assay platform applied. Confidence was low for one review and critically low for six. Conclusions: Procalcitonin is a promising adjunct to calcitonin, with better analytical behaviour, but routine combined measurement is not yet supported. The apparent consistency across syntheses reflects a shared and narrow primary literature rather than independent replication, and the absence of an agreed, method-specific threshold remains the main barrier to implementation.