Collisional variant of CD8+ mycosis fungoides and indolent CD8+ lymphoid proliferation

Abstract: CD8+ lymphoid infiltrates of the skin are classified into different subtypes with variable prognoses and treatment options. Here, we present a patient with CD8+ mycosis fungoides who developed CD8+ indolent lymphoid proliferation in a background of conventional plaque stage CD8+ mycosis fungoides. The patient is a 42-year-old man who had long standing hypopigmented patches on the buttocks, back, and lower extremities that were compatible with CD8+ mycosis fungoides. He then developed a solitary indurated raised lesion on the thigh that was clinically disparate to those elsewhere on the skin. The biopsy showed a collision of CD8+ patch stage mycosis fungoides and indolent CD8+ lymphoid proliferation. Clonality studies on each atypical CD8+ component were not performed to prove or disprove a common T-cell clone. A common clone would indicate plasticity of a neoplastic CD8+ T-cell clone to eventuate into these two divergent patterns, a phenomenon that has been observed in other hematologic malignancies. We highlight the unique aspects of this case by analyzing histopathologic features in conjunction with comprehensive immunohistochemical staining.