Morphologically malignant nodular fasciitis with CALD1-USP6 fusion

Area of Science:

• Oncology
• Pathology
• Genetics

Background:

• Nodular fasciitis is typically a benign myofibroblastic tumor known for rapid growth and spontaneous regression.
• While rare, some histologically benign cases of nodular fasciitis have shown metastatic potential, unpredictable by morphology alone.

Observation:

• A 7-year-old male presented with a tumor in his upper extremity exhibiting features of nodular fasciitis, including myofibroblastic cells, myxoid matrix, and giant cells.
• Unusually, the tumor displayed significant nuclear pleomorphism, a characteristic not typically seen in conventional nodular fasciitis.

Findings:

• Fluorescence in situ hybridization detected a USP6 translocation.
• Next-generation sequencing confirmed a novel CALD1-USP6 fusion, with no other detected somatic or germline mutations.

Implications:

• This case represents a morphologically malignant presentation of nodular fasciitis, expanding its recognized spectrum.
• The identification of the CALD1-USP6 fusion provides further molecular insight into the pathogenesis of nodular fasciitis variants.
• Understanding the diverse presentations and genetic landscape of nodular fasciitis is crucial for accurate diagnosis and management.