Extraordinary Case ReportCutaneous Histiocytic Sarcoma With Cellular CannibalismNanri, Aya MD*; Katayama, Eri MD*; Imamura, Taichi MD*; Muto, Ikko MD*; Saruta, Hiroshi MD, PhD*; Akiba, Jun MD, PhD†; Ohshima, Koichi MD, PhD‡; Nakama, Takekuni MD, PhD*; Ohata, Chika MD, PhD*Author Information *Department of Dermatology, Kurume University School of Medicine, Kurume, Japan; †Department of Diagnostic Pathology, Kurume University Hospital, Kurume, Japan; and ‡Department of Pathology, Kurume University School of Medicine, Kurume, Japan. Correspondence: Chika Ohata, MD, PhD, Department of Dermatology, Kurume University School of Medicine, 67 Asahimachi, Kurume, Fukuoka 830-0011, Japan (e-mail: firstname.lastname@example.org). The authors declare no conflicts of interest. The American Journal of Dermatopathology: April 2020 - Volume 42 - Issue 4 - p 286-291 doi: 10.1097/DAD.0000000000001525 Buy Metrics Abstract Cutaneous histiocytic sarcoma (HS) is a rare malignant tumor. An 82-year-old woman presented with a 4 × 2-cm irregular-shaped red nodule on the left posterior scalp. A biopsy specimen revealed sheets of pleomorphic atypical cells in the dermis and subcutis. A diagnosis of HS was made based on the results of a panel of immunohistochemical stains that revealed positivity of leukocyte common antigen, CD4, CD163, and HLA-DR. At the time of resection, the tumor grew rapidly to 12 × 6.5 × 5 cm in size in 2 months. The resected tumor comprised round, oval, plasmacytoid, and spindled cells. Signet-ring cell type tumor cells were also observed. The histiocytic nature of HS was confirmed owing to the presence of cellular cannibalism, emperipolesis, Langhans giant cell–like cells, Touton giant cell–like cells, foreign-body giant cell–like cells, and hemosiderin laden cells. In some foci, a storiform pattern and fascicular pattern were occasionally observed. Local recurrence occurred shortly after resection. Subsequent radiation therapy showed insufficient effectiveness. It is challenging to make a diagnosis of HS without performing immunohistochemical studies; however, a variety of histiocytic features confirmed in hematoxylin and eosin–stained sections may suggest HS. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.