Cutaneous VCL::ALK fusion ovoid-spindle cell neoplasm

Area of Science:

• Oncology
• Dermatopathology
• Molecular Pathology

Background:

• Recently identified RAS::MAP tyrosine kinase fusion sarcomas often affect deeper tissues.
• Cutaneous sarcomas with VCL::ALK fusion are rare, presenting diagnostic challenges.

Observation:

• An 11-year-old male presented with a pedunculated back papule initially misdiagnosed as pyogenic granuloma.
• Histopathology revealed a unique VCL::ALK fusion spindle (ovoid) cell tumor at the dermis/subcutis interface.
• Microscopic features included spindled and epithelioid cells, myxoid stroma, and focal S100 positivity.

Findings:

• Next-generation sequencing confirmed a VCL::ALK fusion, classifying the tumor as a novel cutaneous RAS::MAP tyrosine kinase fusion sarcoma.
• Differential diagnoses such as epithelioid fibrous histiocytoma were excluded based on specific morphological and immunophenotypic features.
• The tumor exhibited a combination of features distinct from other known VCL::ALK-positive entities.

Implications:

• This case expands the spectrum of RAS::MAP tyrosine kinase fusion sarcomas to include this specific cutaneous VCL::ALK fusion variant.
• Accurate diagnosis requires integrating clinical, histopathological, and molecular findings.
• Understanding these novel fusion sarcomas is crucial for appropriate patient management and therapeutic strategies.