Primary treatment strategies for ATC have included surgical resection combined with radiotherapy, chemotherapy, or concurrent chemoradiation therapy. Despite these aggressive approaches, disease recurrence or progression remains frequently observed. Recent advances in molecular diagnostics and targeted therapy development have expanded treatment options for ATC patients with actionable genetic alterations, such as BRAF mutations or NTRK fusions. Nevertheless, for patients lacking identifiable targetable mutations, therapeutic options remain limited and clinical outcomes are poor. To address this unmet clinical need, the investigators aim to analyze baseline characteristics, treatment outcomes, and biomarker profiles from a larger cohort of ATC patients, with the goal of identification of predictive biomarkers and potential therapeutic targets. Given the rarity of ATC, conducting comprehensive studies at a single institution is challenging. Therefore, the investigators propose to establish a multi-center registry to systematically collect clinical data and tumor specimens from ATC patients.

Thyroid cancers are pathologically classified into differentiated thyroid cancer (DTC),medullary (MTC) and anaplastic carcinoma (ATC). ATC accounts for approximately 1% of thyroid cancer cases in Taiwan and is characterized by its aggressive clinical course with extremely poor prognosis. A subset of patients may present with mixed histology, exhibiting both DTC and ATC components, or may experience progression from DTC to ATC. These cases are typically associated with rapid disease progression and significantly worse clinical outcomes. Because the incidence of ATC is very low, it is not easy to conduct clinical trials with large sample size to investigate novel treatment strategies with some effective treatment modalities reported by case reports or case series. Recently, the genetic test has been reimbursed by our health Bureau for ATC cases. In this study, the investigators aim to enroll ATC patients from multi-centers in Taiwan to collect the baseline characteristics, genetic data, treatment patterns, and clinical outcome of the ATC patients. In addition, the investigators want to collect tumor and blood samples for ATC patients to explore the biomarkers and potential treatment modalities from the real-world data.

Inclusion Criteria:

1. Pathologically or cytologically confirmed ATC and diagnosed after 2015.
2. Capable of understanding and complying with the protocol requirements and signed informed consent. The dead patient can be enrolled without signed informed consent and they were dead before 2025.6.30.

Exclusion Criteria:

1. Inability and unwillingness to give informed consent except dead patient.
2. Patients refuse for collection of clinical data and follow up.

Patients who were pathologically or histologically diagnosed as anaplastic thyroid cancer (ATC) are the target population. The ATC may be transformed from DTC or de novo cases. Anticipated 100 patients.