Diagnosis & Discussion

Diagnosis

Pleomorphic carcinoma, with spindle cell carcinoma and adenocarcinoma components.

Discussion

Pleomorphic carcinomas are malignant epithelial neoplasms composed of discrete populations of spindle cells, giant cells, and/or carcinomatous cells. It is unknown if they represent dedifferentiation of an existing adenocarcinoma or a separate oncogenic pathway. The specimen nicely demonstrates the interface between adenocarcinoma and sarcomatoid components of the tumor (Figure 1; adenocarcinoma left panel, sarcomatoid right panel). This specific tumor demonstrates histiocytic differentiation, making the distinction from histiocytic sarcoma or malignant fibrous histiocytoma difficult. Pleomorphic carcinomas are positive for epithelial cell markers (cytokeratin) and TTF-1; histiocytic carcinomas are not positive for epithelial cell markers. Usually pleomorphic carcinomas are discovered in an advanced clinical stage and are associated with metastasis. When this is the case, pleomorphic carcinoma usually carries a poor prognosis.

The original diagnosis of histiocytic sarcoma on the biopsy specimen demonstrates a pitfall of multiphasic tumors in general: sampling bias often introduces diagnostic error. Histiocytic sarcomas are rare tumors thought to originate from low-grade lymphomas; the patient’s recent history of follicular lymphoma fits the clinical presentation of histiocytic sarcoma nicely. However, in this case, the follicular lymphoma and pleomorphic carcinoma are unrelated. Given the complexity and rarity of histiocytic sarcomas, expert consultation was sought before rendering a diagnosis.

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