Clinical and histopathological appearance of primary cutaneous aggressive epidermotropic cytotoxic T-cell lymphoma with SATB1::FGFR1 fusion. (A) Clinical presentation of rapidly progressing ulcerated lesions on upper extremities and chest. (B) Ulcerated lesions on the left foot showing clinical remission after 4 weeks of therapy with pemigatinib. (C) Skin biopsy. Histological section shows a markedly epidermotropic and adnexotropic lymphoma (original magnification ×40; hematoxylin and eosin [H&E]). (D) The epidermotropic lymphocytes show cytologic atypia and hyperchromasia (original magnification ×200; H&E). (E) The atypical lymphocytes are positive for CD3 (original magnification ×100; immunohistochemistry). (F) The lymphoma cells express CD8 (original magnification ×100; immunohistochemistry). (G) The lymphoma cells express TCR βF1, indicating that the phenotype of the lymphoma cells is α/β (original magnification ×200; immunohistochemistry). (H) The atypical epidermotropic cells are positive for TIA-1, supporting a cytotoxic phenotype of this lymphoma (original magnification ×400; immunohistochemistry).