High-sensitivity cardiac troponin T (hs-cTnT) is the preferred assay for screening for ICI-associated myocarditis due to its superior sensitivity for early detection of myocardial injury, strong association with major adverse events, and ability to identify at-risk patients, including those with overlapping myositis or myasthenia gravis syndromes. The gene discussed is TNNT2; the disease is myositis disease.