The First Case Of The Myopericytomatosis Of The Foot With RAF1 Rearrangement Involving Intron 7 (ATG7-RAF- 1)

Abstract

Abstract Introduction/Objective Myopericytomatosis, recently described by Yin P. Hung et al [1], is an extremely rare myopericytic proliferation with only less than 15 reported cases in the English literature. This neoplasm has been described as dermal or subcutaneous well-circumscribed nodules composed of ovoid to spindled cells in a perivascular distribution, with no significant necrosis, atypia or mitosis. It usually involves the lower extremities with the ankle being the most common location. Next-generation DNA sequencing (NGS) in all the previously reported cases exhibited PDGFRB alterations with no BRAF, NOTCH, and/or GLI1 alterations [1]. Methods We report a 47-year-old man who presented multiple well-encapsulated nodules on his right foot that were localized to the fascia/subcutaneous fat by MRI; fibromas were the main radiologic differential diagnosis. Results The biopsy and subsequent excisional specimens showed diffuse involvement by numerous discrete myopericytomatous nodules composed of bland spindled to ovoid cells. Immunohistochemical staining demonstrated that the myopericytic cells are strongly positive for SMA, focally positive for caldesmon with a patchy cytoplasmic CD99 staining. Ki-67 showed a low proliferation rate of 1–2%. Desmin, CD31, CD34, HHV8, STAT6, S100, HMB45, and Melan-A immunostains were negative. The diagnosis of myopericytomatosis was made. The NGS revealed that the tumor cells are positive for RAF1 rearrangement involving intron 7 (ATG7-RAF-1) with no other findings, including PDGFRB alterations. Conclusion Myopericytomatosis is an exceedingly rare entity with most of the previously reported cases involving the lower extremities and only two cases involving the foot. In all the prior cases, the PDGFRB mutation N666K was noted [1]. We report the first case of RAF1 rearrangement in myopericytomatosis of the foot with no other genetic alterations.