“Cyst” on the forearm of a 28‐year‐old female: Case report of a CIC‐rearranged sarcoma

• Published in: Journal of cutaneous pathology 2019-08, Vol.46 (8), p.599-602
• Main Authors: Lehane, Fiona, Tsikleas, George, Bettington, Andrew, Limarporn, Kunawut, Wilkinson, Lisa, Lehane, Katie
• Format: Article
• Language: English
• Subjects: Adult; atypical Ewing sarcoma; Case reports; CD99 antigen; Cell differentiation; Chromosomes, Human, Pair 19 - genetics; Chromosomes, Human, Pair 19 - metabolism; Chromosomes, Human, Pair 4 - genetics; Chromosomes, Human, Pair 4 - metabolism; CIC; Co-Repressor Proteins - genetics; Co-Repressor Proteins - metabolism; Cysts; Cytoplasm; Diagnosis; Epidermal Cyst - genetics; Epidermal Cyst - metabolism; Epidermal Cyst - pathology; Ewing sarcoma; Ewing's sarcoma; Ewing‐like sarcoma; Female; Forearm; Gene Rearrangement; Homeodomain Proteins - genetics; Homeodomain Proteins - metabolism; Humans; In Situ Hybridization, Fluorescence; Neoplasia; Oncogene Proteins, Fusion - genetics; Oncogene Proteins, Fusion - metabolism; Proto-Oncogene Proteins c-ets - genetics; Proto-Oncogene Proteins c-ets - metabolism; Repressor Proteins - genetics; Repressor Proteins - metabolism; round cell sarcoma; Sarcoma, Small Cell - genetics; Sarcoma, Small Cell - metabolism; Sarcoma, Small Cell - pathology; Skin Neoplasms - genetics; Skin Neoplasms - metabolism; Skin Neoplasms - pathology; Soft tissues; Transcription; Translocation, Genetic; Ultrasound; WT1 Proteins - genetics; WT1 Proteins - metabolism
• ISSN: 0303-6987; 1600-0560
• DOI: 10.1111/cup.13478

Capicua transcriptional repressor (CIC)‐rearranged sarcomas are part of the group of Ewing‐like sarcomas or atypical Ewing sarcomas which, thanks to the progress in molecular diagnosis, are being defined by particular genetic abnormalities separating this group into distinct entities with their own particular histological and immunohistochemical features, as well as different survival outcomes. We report the case of a healthy 28‐year‐old female presenting with a tender lesion on her forearm which after ultrasound examination was clinically favored to represent an infected sebaceous cyst. Hematoxylin‐eosin staining showed a lobulated neoplasm within the subcutis composed of poorly differentiated epithelioid to round cells with a small amount of amphophilic cytoplasm. Frequent mitotic figures and tumor necrosis were present. Immunohistochemical studies showed patchy focal CD99 membranous positivity, negative WT1 and TLE1 staining and diffuse nuclear positivity for ETV4 (performed at outside laboratory). FISH analysis showed significant CIC rearrangement enabling a final diagnosis of an undifferentiated small round cell sarcoma harboring the t(4;19)(q35;q13.1) and CIC‐DUX4 fusion. This case shows the importance of awareness of this entity as, unlike Ewing sarcoma, these lesions present in the soft tissues rather than bone and may, as in this case, arise in the superficial soft tissues and be submitted to a dermatopathology practice.