Renal cell carcinoma metastasizing to solitary fibrous tumor of the pleura: a case report

Abstract

Introduction: A tumor metastasizing to another malignancy is an uncommon phenomenon. Since it was first described in 1902, there have been fewer than 200 cases reported in the literature, with lung cancer metastasizing to renal cell carcinoma being the most frequently described pattern. Here we report a case of a solitary fibrous tumor of the lung acting as the recipient for a renal cell carcinoma. To our knowledge, this is the first reported case of such a combination and the second case involving a solitary fibrous tumor.

Case presentation: A 58-year-old Caucasian man who developed a persistent dry cough presented to our hospital. Imaging studies revealed a large pleural-based mass in the left lung. A biopsy of the mass showed a spindle-cell lesion consistent with a solitary fibrous tumor. The patient underwent surgical excision of the 13 cm mass. The pathological examination confirmed the diagnosis of a solitary fibrous tumor but also demonstrated discrete foci of metastatic renal cell carcinoma. Until that point, a primary renal cell carcinoma tissue diagnosis had not been made and the initial radiological work-up was inconclusive.

Conclusion: Awareness of the unusual phenomenon of tumor-to-tumor metastasis is important for practicing surgical pathologists, particularly in the evaluation of a mass lesion showing bimodal histology. This case also highlights the importance of careful examination of surgical specimens, as minute and unusual findings can direct patient care.

Figure 1

Computed tomographic scan revealing a large pleural-based mass in the left hemithorax.

Figure 2

Positron emission tomographic scan. The left pleural mass showed only diffuse low-level fluorodeoxyglucose (¹⁸F-FDG) uptake of the mass. However, there was a focus of moderate ¹⁸FFDG activity in the superior aspect of the lesion, which was worrisome for malignancy.

Figure 3

Histologic and immunophenotypic characteristics of the tumor. (a) Sections of pleural-based solitary fibrous tumor showing a cellular spindle-cell neoplasm with a patternless architecture and "staghorn" vessels. (b and c) A nodular collection of epithelioid clear cells was incidentally found within the tumor. (d) These cells are negative for CD34 (in contrast to the solitary fibrous tumor on the left), but immunoreactive with (e) broad-spectrum cytokeratin, (f) vimentin, (g) CD10 and (h) paired box gene 2 (PAX2).