Background: Low-grade myofibroblastic sarcoma (LGMS) represents a rare soft tissue neoplasm with a predilection for the head and neck. Intra-abdominal LGMS are rare with only four unequivocal examples reported so far.
Methods: We herein analysed two cases by histological, immunohistochemical, ultrastructural and molecular genetic methods.
Results: Patients were females aged 71 and 66 years. The tumours arose in the mesentery and the pelvic peritoneum. Both revealed features intermediate between conventional fibrosarcoma and leiomyosarcoma with fascicles of spindled, stellated or plump cells possessing fusiform indented vesicular nuclei and pale-eosinophilic cytoplasm. Mitotic activity ranged from 1 to 15 per 10 HPFs. The tumour cells strongly expressed vimentin, variably α-SMA and fibronectin, but were negative for CD117, S-100, desmin, h-caldesmon, β-catenin, ALK-1, MDM2, PDGFRα and PDGFRβ. One tumour showed a weak expression of CD34. Molecular analysis revealed a wild-type KIT exons 9, 11 and 13 and PDGFRA exons 12 and 18. Both patients developed multiple peritoneal recurrences at 5, 13, 25, and 10, 19, 25, 32 months and were alive at 25 and 32 months, respectively. Distant metastases were not detected.
Conclusion: Abdominopelvic LGMS follows a more aggressive clinical course characterised by a higher propensity for local recurrence, contrasting their more superficially located counterparts. LGMS may mimic KIT-negative GIST and a variety of benign and low-grade malignant neoplasms and might be under-recognised.
- myofibroblastic sarcoma
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