Nodular Fasciitis With Malignant Morphology and a <i>COL6A2–USP6</i> Fusion: A Case Report (of a 10-Year-old Boy)
Tess Tomassen, Cornelis P. van de Ven, Jakob Anninga, Christian Koelsche, Laura S. Hiemcke‐Jiwa, Simone A. J. ter Horst, Wendy W. de Leng, Franck Tirode, Marie Karanian, Uta Flucke
Abstract
Nodular fasciitis is usually a benign lesion genetically characterized by ubiquitin-specific protease 6 ( USP6) rearrangements. We present a case of a 10-year-old boy with a 1.5-week history of a painless mass on the right chest wall, which was excised. A histomorphologically malignant tumor with pronounced pleomorphism, atypical mitotic figures, and a myoid immunophenotype was observed. The methylation profile was consistent with nodular fasciitis and fluorescence in situ hybridization confirmed USP6 rearrangement. Using Archer Fusion Plex (Sarcoma Panel) and RNA sequencing, a collagen, type VI, alpha 2 ( COL6A2) –USP6 gene fusion was subsequently identified. Furthermore, DNA clustering analysis also showed a match with nodular fasciitis. During the follow-up of 22 months, no recurrence or metastasis occurred. In conclusion, we describe a clinically benign, histomorphologically malignant mesenchymal neoplasm with a myoid immunophenotype, and a genetic and epigenetic profile consistent with nodular fasciitis. In such cases, molecular analysis is a useful adjunct to avoid unnecessary overtreatment.