Renal adenocarcinoma-associated erythrocytosis in a cat: clinicopathological features and immunohistochemical results

Abstract

This report documents a case of secondary inappropriate erythrocytosis in a cat with renal cell adenocarcinoma, its stabilization through manual erythrocytapheresis, and the EPO-immunostaining on the affected kidney. An 11-year-old cat was presented with lethargy, weight loss and polyuria/polydipsia. An abdominal mass was detected upon physical examination. Clinicopathological work-up revealed marked erythrocytosis (HCT value 64.8%), renal azotemia and decreased urine specific gravity (USG). An abdominal ultrasound was performed, localizing the mass in the right kidney. Serum erythropoietin (EPO) was above the reference interval (RI), and the cytology of the mass was indicative of renal carcinoma. Manual erythrocytapheresis was performed in order to stabilize the patient before surgery, improving the cat's clinical and clinicopathological condition. After nephrectomy, EPO and creatinine concentrations returned within the RI, while the USG markedly increased. Histopathology confirmed the diagnosis of renal adenocarcinoma. Immunohistochemistry with anti-EPO antibody revealed diffuse and strong cytoplasmatic positivity in tumor cells.

Keywords: Erythropoietin; Feline; Immunohistochemistry; Manual erythrocytapheresis; Renal neoplasia.

Fig. 1

Fine-needle aspirate from a renal mass in a cat. Poorly cellular and hemodiluted sample, with large three-dimensional clusters of moderately pleomorphic epithelial cells with variable nucleus/cytoplasmic ratio, moderate anisokariosis and prominent nucleoli (May-Grunwald-Giemsa stain; Bar=50 μm).

Fig. 2

Gross appearance and histopathology of a feline renal mass. (A): Surgically resected kidney. The tumor mass has completely invaded cortex and medulla of the cranial pole; on section, the tumor tissue is non-capsulated and composed of multiple red lobules embedded in a dark red gelatinous tissue (Bar=2.5 cm). (B): Moderately pleomorphic epithelial cells arranged in irregular tubules and papillae, consistent with tubulo-papillary renal cell carcinoma (Hematoxylin and eosin stain; Bar=50 μm).

Fig. 3

Immunohistochemistry for erythropoietin (EPO) expression. Diffuse and intense cytoplasmic immunostain for EPO in tumor cells (A: Bar=50 µm) and in tubular cells of non-neoplastic renal tissue adjacent to the carcinoma (B: Bar=100 µm).