Background: Anaplastic thyroid carcinoma (ATC) is a rare and frequently fatal type of thyroid cancer. The degree of heterogeneity in survival rates for ATC is incompletely studied. This study evaluated the factors associated with overall survival (OS) of patients with ATC using multicenter real-world data from a national tertiary care center network in France. Methods: In this multicenter, retrospective cohort study, all patients with ATC diagnosed between 2010 and 2020 were identified from the national database of the French ENDOCAN-TUTHYREF network. Factors associated with OS were examined in multivariable analyses using Cox proportional hazards models. Results: The study included 360 patients. Of these, 220 (61%) were female and the median age was 72 years (interquartile range: 62-80). The percentages of patients with pure and mixed (synchronously-transformed) ATC (p-ATC and st-ATC) were 62.5% and 26.7%, respectively. The median OS was 6.8 months [confidence interval, CI: 5.5-8.1]: not reached for stage IVa, 11.4 months [8.2-17.8] for IVb, and 4.6 months [3.5-5.7] for IVc. Surgery, radiation therapy to the neck, chemotherapy, and best supportive care were administered to 69 (19.2%), 214 (59.4%), 254 (70.6%), and 66 (18.3%) patients, respectively. In a multivariable analysis, including stage IVb-IVc patients, significantly higher OS was observed in patients with Eastern Cooperative Oncology Group performance-status of 0-1 (hazard ratio [HR], 0.6; [CI, 0.4-0.9], p < 0.02), stage IVb [HR, 0.5; CI, 0.4-0.8, p < 0.001], and multimodal treatment (surgery and chemoradiotherapy) [HR, 0.07; CI, 0.04-0.1, p < 0.001]. Variables associated with significantly worse OS included: p-ATC (vs. st-ATC) [HR, 1.83; CI, 1.33-2.51, p = 0.001] and a neutrophil-to-lymphocyte ratio (NLR) >5.05 [HR, 2.05, CI, 1.39-3.05, p < 0.001]. Conclusions: Factors independently associated with improved OS in ATC included: European Cooperative Oncology Group performance status, disease stage, multimodality treatment, synchronously transformed ATC, and lower NLR. Long-term OS was observed in selected patients with ATC who underwent multimodal treatment.

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