Abstract

We present a case of an 8-month-old female presenting with a congenital CD34+ spindle cell tumor on the scalp with a novel PLEKHH2-ALK fusion. The patient presented with 2.0 cm pink, smooth nodule. MRI demonstrated a scalp lesion with transosseous extension through the subjacent frontal bone with dural involvement. Histologic sections demonstrated an infiltrative dermal neoplasm composed of monomorphic spindle cells in a storiform pattern. By immunohistochemistry, the lesional cells were diffusely CD34 positive and negative for SMA, desmin, SOX-10, S-100, myogenin, and EMA. FISH testing failed to demonstrate a rearrangement of PDGFB, raising the question of a PDGFB-negative dermatofibrosarcoma protuberans. A next generation sequencing fusion panel demonstrated a PLEKHH2-ALK gene fusion. Subsequent immunohistochemical staining for ALK showed patchy positivity in the spindle cells. While the clinical and histologic features were reminiscent of dermatofibrosarcoma protuberans, this lesion harbors a previously undescribed PLEKHH2-ALK fusion. Therefore, this may represent a previously unrecognized soft tissue tumor that clearly has the potential for at least locally aggressive behavior. This novel rearrangement may also have treatment implications, as tumors with ALK fusions may respond to targeted therapy with ALK inhibitors. Dermatopathologists may consider including immunohistochemical stains for ALK in the evaluation of CD34-positive tumors and cases with histopathologic features of dermatofibrosarcoma protuberans in order to potentially identify additional cases that may harbor this fusion.

Financial Disclosure:
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