Biomarker testing in patients diagnosed with advanced/metastatic medullary thyroid cancer in the USA.

To describe real-world testing patterns for in US patients with advanced/metastatic medullary thyroid cancer and determine consistency of real-world testing practices with national guidelines. The authors performed a retrospective medical record analysis of patients with advanced/metastatic medullary thyroid cancer who initiated systemic therapy between 2013 and 2018. Seventy-five US-based oncologists collected the data using a customized electronic data collection form. A total of 59.6% (121 of 203) of patients underwent testing for , and 37.2% (45 of 121) had a mutation, of which 55.6% were identified as mutation-positive before initial diagnosis. Overall, 90 (44.3%) patients were tested for biomarkers on or after initial diagnosis, with being the most tested (95.6%) biomarker. The authors' findings suggest an opportunity to improve testing rates in accordance with treatment guidelines.