NTRK1 and mesenchymal cell neoplasm: Although panTRK immunohistochemistry is relatively sensitive for mesenchymal tumors with NTRK1/2/3 fusions [49–52], it demonstrates imperfect specificity in skin and soft tissue mesenchymal tumors, as it can be positive in other neoplasms such as those with neural or myogenic differentiation [51, 52].