Pleomorphic hyalinizing angiectatic tumor (PHAT) of soft parts and hemosiderotic fibrolipomatous tumor (HFLT) are two rare low-grade locally recurring neoplasms with predilection for the foot/ankle. Recent studies support a close link between the two entities, and origin of PHAT from HFLT and occurrence of hybrid HFLT/PHAT have been documented. Both lesions often harbor TGFBR3 or MGEA5 rearrangements. Rare sarcomas originating from HFLT/PHAT have been reported, typically resembling myxofibrosarcoma or myxoinflammatory fibroblastic sarcoma. We describe a novel SMARCA4-deficient undifferentiated sarcoma with rhabdoid features originating from hybrid HFLT/PHAT in the foot of a 54-year-old male. The tumor pursued a highly aggressive course with rapid regrowth after resection and multiple metastases resulting in patient’s death within 5 months, despite systemic chemotherapy. Immunohistochemistry revealed SMARCA4 loss in the undifferentiated sarcoma, but not in the HFLT/PHAT. Molecular testing confirmed TGFBR3/MGEA5 rearrangements. This report expands the phenotypes of sarcomas developing from pre-existing PHAT/HFLT.

软部多形性透明化血管扩张性肿瘤 (PHAT) 和含铁血黄素纤维脂肪瘤 (HFLT) 是两种罕见的低度局部复发性肿瘤，好发于足部/踝部。最近的研究支持这两个实体之间的密切联系，并且已经记录了来自 HFLT 的 PHAT 的起源和混合 HFLT/PHAT 的发生。两个病变通常都含有TGFBR3或MGEA5重排。已经报道了源自 HFLT/PHAT 的罕见肉瘤，通常类似于粘液纤维肉瘤或粘液炎性纤维母细胞肉瘤。我们描述了一种新型 SMARCA4 缺陷未分化肉瘤，其横纹肌特征源自一名 54 岁男性脚部的混合 HFLT/PHAT。尽管进行了全身化疗，但肿瘤仍呈高度侵袭性，切除后迅速再生，多发转移导致患者在 5 个月内死亡。免疫组织化学显示未分化肉瘤中有 SMARCA4 丢失，但在 HFLT/PHAT 中没有。分子测试证实了TGFBR3/MGEA5重排。本报告扩展了从预先存在的 PHAT/HFLT 发展而来的肉瘤的表型。