In the WHO 2022 Classification of Soft Tissue Tumours, NTRK-rearranged spindle cell neoplasms have been recognized as a distinct entity. Which statement about this entity is MOST accurate?

• A They exclusively occur in the head and neck of infants, never in adults
• B NTRK3 fusion with ETV6 is pathognomonic and exclusively diagnostic in all age groups
• C Pan-TRK IHC shows exclusively nuclear staining pattern regardless of fusion partner
• D They demonstrate lipofibromatosis-like morphology in infants but may show higher-grade features in adults, with diagnostic pan-TRK IHC showing cytoplasmic positivity ✓

Explanation

NTRK-rearranged spindle cell neoplasms recognized in WHO 2022 show a morphological spectrum: lipofibromatosis-like pattern in infants and higher-grade spindled or round cell morphology in adults, with variable sites of occurrence. Pan-TRK IHC typically shows cytoplasmic and/or nuclear positivity depending on the fusion partner — ETV6-NTRK3 causes nuclear staining, while other fusions cause cytoplasmic staining. ETV6-NTRK3 is characteristic of infantile fibrosarcoma/secretory carcinoma but is not pathognomonic across all NTRK entities. These tumors can occur in many anatomical sites and in adults.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.