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primitive myxoid mesenchymal tumor of infancy

Tuesday 4 April 2006


- infants or neonates (50%)
- localization: trunk, extremities, and head and neck
- nonencapsulated tumors
- multinodular appearance
- focal infiltrative growth
- white fleshy cut surface
- tumor diameter ranging from 2 to 15 cm
- diffuse growth
- primitive spindle cells or polygonal cells or round cells
- myxoid background
- vaguely nodular pattern
- peripheral collagenized stroma
- higher cellularity at the periphery
- delicate vascular network in the background


- diffuse reactivity for vimentin
- no reactivity for smooth muscle actin, muscle specific actin, desmin, S-100 protein, or myogenin

Electron microscopy

- poorly differentiated fibroblastic proliferation


- Chr.Y rearrangements
- Chr.9 rearrangements
- Chr.3 rearrangements

Differential diagnosis

- soft tissue sarcomas

  • embryonal rhabdomyosarcoma
  • Ewing sarcoma/primitive neuroectodermal tumor
  • congenital infantile fibrosarcoma
  • primitive sarcomas


- possible recurrences
- possible metastasis


- Alaggio R, Ninfo V, Rosolen A, Coffin CM. Primitive myxoid mesenchymal tumor of infancy: a clinicopathologic report of 6 cases. Am J Surg Pathol. 2006 Mar;30(3):388-94. PMID: 16538060