Basaloid squamous carcinoma metastatic to renal-cell carcinoma: fine-needle aspiration cytology of tumor-to-tumor metastasis.

We describe an unusual case of a basaloid squamous-cell carcinoma (BSCC) of the tonsil in a 56-yr-old man that metastasized to a primary renal-cell carcinoma (RCC) and the lung. The diagnosis of the second primary, the RCC, was based on fine-needle aspiration (FNA) cytology. A subsequent nephrectomy specimen revealed BSCC metastatic to RCC, clear-cell type. Retrospective analysis of the FNA of the renal mass revealed classic RCC morphology and, in addition, another cytologically distinctive pattern characterized by occasional sheets of cohesive neoplastic cells with hyperchromatic nuclei and nuclear molding representative of BSCC. The cytologic features of a subsequent FNA of the lung were characteristic of metastatic BSCC. Our retrospective analysis of cytologic material from the renal mass underscores the importance of raising the possibility of tumor-to-tumor metastasis when distinctly different morphologic features are seen in an otherwise typical cytology of a neoplasm in patients with an already known or suspected second primary. To our knowledge, this case report is the first one documenting metastasis of BSCC to RCC.