Primitive Multipotential Primary Sarcoma of Bone (Polyhistioma) or Carcinosarcoma metastatic to bone?

Abstract

The pictures shown were taken from an axillary lymph node of a 33-year-old man who presented with an ovoid lesion (1.6 cm in diameter) in the proximal aspect of the left femur, an ulcerated lesion in the skin of right forearm, and axillary lymphadenopathy. A biopsy of the axillary lymph node was performed. This showed massive metastatic involvement by a largely undifferentiated neoplasm composed of smallto medium-sized round cells with focal rhabdoid features, associated with foci of bone formation and squamous differentiation (Figures 1-3). Under the assumption that the femoral lesion was the primary tumor and that the skin and axillary node represented metastatic deposits, the diagnosis was in favor of primitive multipotential primary sarcoma of bone (polyhistioma). First described by Hutter et al in 1966, this exceptionally rare neoplasm can affect long or flat bones. Microscopically, it is characterized by a predominantly undifferentiated appearance combined with various types of mesenchymal and epithelial differentiation, including osteoid, vascular, chondroid, and squamous. In 1977, Jacobson coined the term polyhistioma to designate a related if not identical malignant small cell neoplasm of bone and soft tissues with the capacity to differentiate into several types of mesenchymal (but not epithelial) tissues. A case very similar to ours was reported by Frydman et al in 1991. It was characterized by the focal presence of osseous and epithelial elements (confirmed by immunohistochemical staining) in an otherwise undifferentiated neoplasm of the tibia.