Low-grade fibromyxoid sarcoma (LGFMS) is a malignancy with propensity for late relapse that principally affects deep soft tissues of the extremities and trunk. Its occurrence in the lower female genital tract is rare, and thus it may not be always considered in the differential diagnosis. We describe the salient features of 7 vulvovaginal LGFMS identified in the authors’ consultation files. Clinical information was obtained from referring pathologists. Archival slides were reviewed, and immunohistochemistry and fluorescence in situ hybridization were performed in cases with available material. Median age was 40 years (range, 34 to 58 y). Primary sites included vulva (n=6) and vagina (n=1). Tumors were 1.2 to 8.7 cm (median, 5.0 cm) in size and grossly circumscribed with firm to focally gelatinous cut surfaces. Microscopically, 5/7 had infiltrative edges. All tumors showed fibrous and myxoid areas, with lobulated myxoid foci in 5/7, comprising storiform, patternless, or (less often) fascicular arrangement of spindled to stellate cells with bland, slender to ovoid nuclei. In all cases, mitoses were <1/2.4 mm², and necrosis was absent. Capillary “arcades” were seen in 3/7. Margins were positive in 3/6. Immunohistochemistry showed positive epithelial membrane antigen in 4/6 and MUC4 in 5/6. Fluorescence in situ hybridization detected FUS rearrangement in 5/7. Both tumors without FUS rearrangement were also negative for EWSR1 rearrangement. All 5 patients with available follow-up were alive and disease-free 10 to 150 months (median, 57 mo) after diagnosis. However, a review of vulvovaginal/pelvic LGFMS previously reported shows recurrences as late as 45 years after initial diagnosis. Pathologists need to be aware that LGFMS can arise in the vulvovaginal region. Tumor lobulation, capillary arcades, and positive MUC4 are helpful features distinguishing LGFMS from other bland myxoid spindle cell neoplasms in the lower female genital tract. Molecular testing can be useful in challenging cases. Complete excision is feasible for most vulvovaginal LGFMS. Long-term surveillance is required as local and/or distant spread can occur decades after diagnosis.

低级别纤维粘液样肉瘤 (LGFMS) 是一种具有晚期复发倾向的恶性肿瘤，主要影响四肢和躯干的深部软组织。它发生在女性下生殖道的情况很少见，因此在鉴别诊断中可能并不总是考虑到它。我们描述了作者咨询文件中确定的 7 种外阴阴道 LGFMS 的显着特征。临床信息来自转诊病理学家。对档案载玻片进行了审查，并在有可用材料的情况下进行了免疫组织化学和荧光原位杂交。中位年龄为 40 岁（范围为 34 至 58 岁）。主要部位包括外阴（n=6）和阴道（n=1）。肿瘤大小为 1.2 至 8.7 厘米（中位数为 5.0 厘米），并具有坚硬至局部凝胶状切割表面的大体边界。显微镜下，5/7 有浸润边缘。所有肿瘤均显示纤维和粘液样区域，5/7 有分叶状粘液样病灶，包括梭形、无图案或（较少见）束状排列的梭形至星状细胞，核平淡、细长至卵圆形。在所有情况下，有丝分裂<1/2.4 mm²，无坏死。毛细血管“拱廊”出现在 3/7。3/6 的利润率为正。免疫组化显示4/6阳性上皮膜抗原和5/6阳性MUC4。荧光原位杂交检测到5/7 的FUS重排。两个没有FUS重排的肿瘤对EWSR1也是阴性的重排。在诊断后 10 至 150 个月（中位数为 57 个月），所有 5 名可进行随访的患者均存活且无病。然而，先前报道的外阴阴道/盆腔 LGFMS 的回顾显示，最晚在初次诊断后 45 年复发。病理学家需要意识到 LGFMS 可能出现在外阴阴道区域。肿瘤分叶、毛细血管拱廊和阳性 MUC4 是区分 LGFMS 与下女性生殖道其他温和的粘液样梭形细胞肿瘤的有用特征。分子测试在具有挑战性的情况下很有用。对于大多数外阴阴道 LGFMS，完全切除是可行的。需要进行长期监测，因为局部和/或远处传播可能在诊断后数十年发生。