EXPRESS: Microwave ablation of a primary renal tumor in a cat

An 11-year-old male neutered domestic shorthair cat with pre-existing IRIS stage two chronic kidney disease and paraneoplastic polycythemia was presented for evaluation of a left renal mass. Cytology was consistent with nephroblastoma, well-differentiated carcinoma, adenoma, or papilloma. Due to the cat's compromised renal function, nephrectomy was considered high risk and ultrasound-guided microwave ablation (MWA) was performed as a nephron-sparing alternative. The procedure was well tolerated without immediate complications. Renal values remained stable throughout follow-up, and the paraneoplastic polycythemia resolved following ablation. A delayed complication of recurrent abscess and fistula formation at the probe insertion site extending along the body wall occurred, but resolved with surgical debridement, drainage, and an extended course of antibiotic therapy. Near-total resolution of the renal mass was confirmed on follow-up ultrasound, and the cat remained clinically well 462 days post-ablation without evidence of recurrence or metastasis. Relevance and novel information: Primary renal tumors in cats are uncommon and nephrectomy is the recommended treatment; however, it may be contraindicated in cats with concurrent renal disease. There is no established role for chemotherapy in feline primary renal tumors, leaving limited options for cats that cannot undergo surgery. While MWA is widely used in human medicine for small renal tumors and has been reported in other tumor types in dogs, it has not been described in cats. This case demonstrates that MWA may be a feasible and potentially effective nephron-sparing treatment option for feline primary renal tumors, and that MWA may be effective at resolving paraneoplastic polycythemia in cases where nephrectomy may be contraindicated.