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Home > G. Tumoral pathology > ectomesenchymoma


Friday 29 February 2008

Definition: Malignant ectomesenchymoma (MEM) represents a heterogeneous group of tumors, most likely originating from pluripotent primitive neural crest cells.


- malignant mesenchymal tumor (typically RMS) with neuroblastic component


- Tumor composed of neuroectodermal and mesenchymal elements
- Usually variably differentiated neuroblastoma plus rhabdomyosarcoma
- Postulated to recapitulate neural crest-derived ectomesenchyme
- Usually childhood
- Aggressive neoplasm
- variable neural elements: Neuroblasts, ganglion cells, Schwann cells
- rhabdomyosarcoma component:Spindled or rounded rhabdomyoblasts
- ganglion cells
- classic embryonal rhabdomyosarcoma (ERMS)
- ganglioneuroma components
- No specific molecular genetic abnormality
- Postulated to recapitulate neural crest-derived ectomesenchyme
- Rhabdomyosarcoma can metastasize as ectomesenchymoma


- Incidence: Very rare
- Age

  • Usually childhood (Under age of 4 years)
  • Exceptionally in adults


- Head and neck

  • Nasal cavity
  • Orbit
  • Central nervous system

- Abdomen
- Genitourinary tract
- Paratesticular region
- Extremities


- Rapidly growing mass


- Aggressive neoplasm
- Poor outcome


- Variably sized
- Infiltrative
- Hemorrhage and necrosis


- Variable neural component
- Ganglioneuroma

  • Ganglion cells in variable numbers
  • Differentiated Schwann cells in fascicles or whorls
  • Rarely malignant peripheral nerve sheath cells

- Rarely neuroblastic element

  • Nodules of small darkly staining cells

- Mesenchymal component

  • Rhabdomyosarcoma
    • Sheets, nests, or cords of small round cells
    • Spindled or rounded rhabdomyoblasts with eosinophilic cytoplasm
  • Rarely other elements, e.g., chondrosarcoma

- Components are typically intermingled, not discrete
- Lacks pleomorphism

Cytogenetic analysis

- +2, -6, +11, +20
- hyperploidy
- 6p21 amplification (HMGA1 locus)
- 6p11.2 amplification

Molecular genetics

- No specific molecular genetic abnormality known.

Gene Expression Profiling

- Some CNS cases show overlap with malignant peripheral nerve sheath tumor

Differential diagnosis

- Rhabdomyosarcoma

  • Typical patterns of embryonal or alveolar subtype
  • Absence of neural component
  • Characteristic genetic findings in alveolar rhabdomyosarcoma

- Malignant Triton Tumor

  • Malignant nerve sheath cells predominate
  • Lacks neuroblastomatous component
  • Lacks ganglion cells

- Neuroblastoma

  • Lacks rhabdomyosarcomatous component

- Ganglioneuroma

  • Mixture of Schwann cells and mature ganglion cells
  • Lacks rhabdomyoblastic component
  • Lacks neuroblastomatous component

Molecular biology

- HRAS mutation

  • Frequent HRAS Mutations in Malignant Ectomesenchymoma: Overlapping Genetic Abnormalities With Embryonal Rhabdomyosarcoma. (26872011)

Paywall References

- Frequent HRAS Mutations in Malignant Ectomesenchymoma: Overlapping Genetic Abnormalities With Embryonal Rhabdomyosarcoma.
Huang SC, Alaggio R, Sung YS, Chen CL, Zhang L, Kao YC, Agaram NP, Wexler LH, Antonescu CR. Am J Surg Pathol. 2016 Jul;40(7):876-85. doi : 10.1097/PAS.0000000000000612 PMID: 26872011

- Floris G, Debiec-Rychter M, Wozniak A, Magrini E, Manfioletti G, De Wever I, Tallini G, Sciot R. Malignant ectomesenchymoma: genetic profile reflects rhabdomyosarcomatous differentiation. Diagn Mol Pathol. 2007 Dec;16(4):243-8. PMID: 18043289

- Molecular array analyses of 51 pediatric tumors shows overlap between malignant intracranial ectomesenchymoma and MPNST but not medulloblastoma or atypical teratoid rhabdoid tumor. Kleinschmidt-DeMasters BK et al: Acta Neuropathol. 113(6):695-703, 2007

- Rhabdomyosarcoma metastasizing as a malignant ectomesenchymoma. Edwards V et al: Ultrastruct Pathol. 23(4):267-73, 1999

- Malignant ectomesenchymoma in childhood. Mouton SC et al: Pediatr Pathol Lab Med. 16(4):607-24, 1996