Extrarenal Rhabdoid Tumor

Definition

Neoplasm composed of large noncohesive cells with keratin positive paranuclear inclusions
Other recognized types of neoplasms must be excluded

Sheets of poorly cohesive cells
Large polygonal or spindled cells
Abundant glassy eosinophilic cytoplasm
- Paranuclear eosinophilic inclusions
  - May be focal or widespread, occasionally not easy to find
  - May be weakly PAS positive
  - Keratin positive
  - Usually vimentin positive
Large eccentric vesicular nucleus
- Round or bean shaped
- Large, prominent nucleolus
Mitotic rate frequently high
Other neoplasms must be excluded
- Particularly, metastatic carcinoma and melanoma must be excluded
- Specifically, a strict definition does not permit reactivity for:
  - Desmin, actin or myoglobin
    - Neoplasms with positivity of these markers should be diagnosed as rhabdomyosarcoma even if keratin positive
  - S100
  - Neurofilament
- Neoplasms not fulfilling all of these strict criteria may be designated as malignant neoplasm with rhabdoid features
Extrarenal rhabdoid tumor is histologically identical to renal rhabdoid tumor

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342