自发性绒毛膜癌是一种罕见的、高度血管化的恶性滋养细胞肿瘤，发生在人类和动物中。本报告描述了来自圈养繁殖群的 4 只经产但未妊娠的 Amargosa 田鼠（Microtus californicus scippensis）的皮下组织中异常自发出现的 4 种绒毛膜癌。两种皮下肿瘤由纤维血管基质内的中型至大型滋养细胞和细胞滋养细胞的多灶性不粘性和浸润性聚集体组成。肿瘤细胞与不同大小的血栓和出血和坏死的空洞区域相关。两个皮下肿瘤主要由膨胀的、充满血液的囊性空间组成，内衬肿瘤性细胞滋养层，偶尔含有中型至大型滋养层。在所有 4 个肿瘤中，滋养层和细胞滋养层全细胞角蛋白和细胞角蛋白 8/18 呈阳性，甲胎蛋白呈阴性，并且含有胞浆内过碘酸希夫 (PAS) 阳性糖原。在具有血绒质胎盘的物种中，滋养层细胞迁移到母体循环中并栓塞到远处的非生殖组织，这可能解释了这 4 种肿瘤的不寻常的皮下分布。 2 个多房性少细胞肿瘤可能代表肿瘤转化的早期阶段。据作者所知，这是第一份描述啮齿动物生殖部位绒毛膜癌特征的报告。

Spontaneous choriocarcinomas are rare, highly vascular, malignant trophoblastic tumors that occur in humans and animals. This report describes the unusual spontaneous presentation of 4 choriocarcinomas within the subcutaneous tissues of 4, multiparous but nongravid, Amargosa voles (Microtus californicus scirpensis) from a captive breeding colony. Two subcutaneous neoplasms were composed of multifocal discohesive and infiltrative aggregates of medium to large trophoblasts and cytotrophoblasts within a fibrovascular stroma. Neoplastic cells were associated with variably sized thrombi and cavitary areas of hemorrhage and necrosis. Two subcutaneous tumors were predominantly composed of expansile, blood-filled, cystic spaces lined by neoplastic cytotrophoblasts and occasionally contained medium to large trophoblasts. Trophoblasts and cytotrophoblasts were positive for pancytokeratin and cytokeratin 8/18, negative for alpha-fetoprotein, and contained intracytoplasmic Periodic acid-Schiff (PAS)-positive glycogen in all 4 tumors. In species with hemochorial placentation, migration of trophoblasts into maternal circulation with embolization to distant nonreproductive tissues occurs and may explain the unusual subcutaneous distribution of these 4 tumors. The 2 multiloculated paucicellular tumors may represent an early stage of neoplastic transformation. To the authors' knowledge, this is the first report characterizing choriocarcinomas in extrareproductive sites in rodents.