Pleomorphic Adenoma-Like Tumor in the Kidney: Case Report of a Rare Mixed Tumor

Abstract

Background: Pleomorphic adenoma is the most common salivary gland tumor and is notably able to metastasize while displaying a benign-appearing morphological appearance, greatly resembling that of the primary tumor.

Case report: Here, we report a case of a 66-year-old male who presented with a 7-month history of a left upper renal mass. Microscopic examination revealed characteristics typical of pleomorphic adenoma, including chondromyxoid stroma and benign ductal and tubular cells. Consequently, a diagnosis of benign mixed tumor resembling a metastasizing pleomorphic adenoma (MPA) to the kidney was made.

Conclusions: We report a rare instance of a tumor resembling pleomorphic adenoma with metastasis to the kidney, the 13^th reported case of kidney metastasis in the literature. This case is additionally the 2^nd case with metastases to the kidney and no known primary salivary gland tumor. We believe that this entity is most consistent with the histopathological findings reported in our case, despite the lack of a patient history of primary salivary gland tumor. We subsequently compare patient outcomes across all known cases of benign MPA to the kidney or PA-like tumors in the kidney with patient outcomes described in a 2015 study that analyzed all cases of MPA in the literature.

Keywords: adenoma; kidney neoplasms; malignant; mixed tumor; neoplasm metastasis; pleomorphic; salivary gland neoplasm.

Figure 1

MRI shows an 8 cm, heterogeneously T₂ hyperintense mass with internal enhancing nodular components.

Figure 2

Photograph showing a 7.5 × 7 × 6 cm tan-white firm mass situated in the upper pole of the kidney. The cut surface of the mass is homogeneous and firm. The mass appears to be encapsulated and abuts the renal parenchyma and does not grossly appear to invade the renal pelvis.

Figure 3

(a) Low-power microscopic image showing the encapsulated pleomorphic adenoma-like tumor in relation to adjacent normal kidney parenchyma (10X magnification). (b) Cellular areas of the tumor including tubular and ductal structures. Image insert: Hypocellular areas of the tumor showing a chondromyxoid stroma (20X magnification). (c) Immunohistochemistry showing positive staining for EMA in the luminal cells of the ducts and tubules (20X magnification). (d) Immunohistochemistry showing positive staining for p63 in the basal cells of the ducts and tubules (20X magnification).