Case Report: First case of low-grade myofibroblastic sarcoma of the vulva during pregnancy

Abstract

Low-grade myofibroblastic sarcoma (LGMFS) of the vulva is exceptionally rare, with only two prior cases reported. We present the third documented case globally and the first occurring during pregnancy, highlighting diagnostic and therapeutic challenges in this unique clinical scenario. A 34-year-old woman presented with a recurrent vulvar mass initially misdiagnosed as angiomyofibroblastoma. The lesion reappeared asymptomatically during pregnancy and was conservatively managed with ultrasound surveillance, followed by term cesarean delivery to mitigate perineal trauma risks. Postpartum evaluation revealed a 3.7 cm T2-hyperintense nodule on MRI. Although intraoperative frozen sections suggested benign margins, definitive histopathology and molecular studies (CD34+/SMA+; FISH-negative for COL1A1::PDGFB fusion and MDM2 amplification) confirmed LGMFS. Radical vulvectomy with 2 cm margins achieved disease-free survival at 17 months without adjuvant therapies. This case underscores that LGMFS may recur silently during pregnancy, necessitating rigorous histopathological re-evaluation of prior benign diagnoses. Multidisciplinary coordination enabled safe deferral of definitive surgery until postpartum without compromising outcomes, while radical excision alone proved curative, reflecting the tumor's indolent biology. Our findings establish the first pragmatic framework for managing vulvar LGMFS in pregnancy, emphasizing tailored surgical planning over routine adjuvant interventions.

Keywords: case report; low-grade myofibroblastic sarcoma; pregnancy; rare tumor; vulvar.

Figure 1

Timeline of the diagnosis and management of the case, illustrating initial discovery, surgical excision, monitoring, recurrence, and follow-up. LGMFS, low-grade myofibroblastic sarcoma; MRI, magnetic resonance imaging.

Figure 2

(A, B) Gross appearance of the vulvar mass (indicated by the red arrow) located on the lower middle portion of the left labium majus, measuring approximately 2 cm in its longest dimension. (C, D) Gross appearance of the excised LGMFS (C) and its cross-section (D). (C) The tumor is firm with an irregular surface and well-defined borders. (D) The cross-section reveals a white, fibrous texture without evidence of hemorrhage or necrosis.

Figure 3

MRI images of LGMFS, indicated by red arrows, in horizontal (left), coronal (middle), and diffusion-weighted imaging (DWI, right) planes, showcasing restricted diffusion and well-defined tumor margins.

Figure 4

Microscopic view of the tumor showing an absence of a capsule and an indistinct boundary with surrounding tissues. Cellular proliferation with prominent mitotic activity is easily identifiable in certain regions.