Kaposi sarcoma (KS) is a rare low-grade angioproliferative neoplasm associated with human herpesvirus 8 (HHV-8) infection with multiple clinical subtypes and varying histopathologic patterns. Histologically, many different variants of KS have been reported, yet all can be difficult to recognize and must be differentiated from other vascular tumors. In this report, we studied fourteen cases of a newly described variant of KS reminiscent of a well-differentiated angiosarcoma (angiosarcoma-like KS). All cases showed a diffuse, ill-defined infiltrative dermal-based lesion composed of numerous anastomosing vascular channels of varying caliber lined by a single layer of endothelium with minimal pleomorphism. The vascular proliferation ramified through the dermis and dissected the collagen bundles along with infiltration into the subcutaneous fat and around skin appendages. All cases showed expression of vascular markers (CD31, CD34, and ERG) and were positive for HHV-8. None showed the classic histopathology associated with KS. Without clinical guidance these tumors can be difficult to recognize as KS, creating significant diagnostic challenges. Our study expands on a rare histologic variant of KS that ought to be considered in the differential diagnosis of any cutaneous well-differentiated angiosarcoma. Awareness of this variant of KS is of important for proper diagnosis and management of these patients; thus, careful attention to the histomorphology and clinical history can help lead the pathologist to the correct diagnosis.

卡波西肉瘤 (KS) 是一种罕见的低度血管增生性肿瘤，与人类疱疹病毒 8 ( HHV-8 ) 感染相关，具有多种临床亚型和不同的组织病理学模式。在组织学上，已报道 KS 的许多不同变体，但所有变体都难以识别，必须与其他血管肿瘤区分开来。在本报告中，我们研究了 14 例新描述的 KS 变体，让人想起分化良好的血管肉瘤（血管肉瘤样 KS）。所有病例均显示弥漫性、边界不清的浸润性真皮病变，由许多不同口径的吻合血管通道组成，内衬单层内皮，具有最小的多形性。血管增殖穿过真皮并解剖胶原束，同时渗透到皮下脂肪和皮肤附属器周围。所有病例均显示血管标志物（CD31、CD34和ERG）表达，且HHV-8呈阳性。没有一个显示出与 KS 相关的经典组织病理学。如果没有临床指导，这些肿瘤可能很难被识别为 KS，从而造成重大的诊断挑战。我们的研究扩展了 KS 的一种罕见组织学变异，在任何皮肤分化良好的血管肉瘤的鉴别诊断中都应考虑到这种变异。了解 KS 的这种变异对于正确诊断和治疗这些患者非常重要；因此，仔细关注组织形态学和临床病史可以帮助病理学家做出正确的诊断。