Sarcoma and mixed epithelial-mesenchimal tumours

Primary malignant sarcomas of the lung are rare, the most common being leiomyosarcoma and malignant fibrohistiocytoma. The distinction between primary and metastatic sarcoma rests on the clinical history.
Immunohistochemistry on cell block material can be useful in the differential diagnosis.

Cytologic diagnostic features

  • Sheet-like, cellular aggregates
  • Single, highly atypical spindle cells

Differential diagnosis

  • Spindle cell carcinoma
  • Spindle cell carcinoid
  • Sarcomatoid mesothelioma
  • Melanoma

Pulmonary blastoma and carcinosarcoma are biphasic tumors, occurring predominantly in the lung periphery and associated with a poor prognosis. Pulmonary blastoma is a malignant tumor composed of primitive glandular and stromal elements, resembling fetal lung. The spindle cell component may show myxoid, chondroid, osteoid or rhabdomyoblastic differentiation; the epithelial component is composed of cuboidal to columnar cells with frequent mitoses. The biphasic cell population is observed on cytologic preparations: spindle-shaped or oval cells with scant cytoplasm and larger, round to columnar epithelial cells.
Carcinosarcoma differs from blastoma in the mean age of the patient at presentation (65 rather than 40 years). The spindle-cell component shows more fibroblast-like differentiation with collagenization.

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