Solitary Masseter Metastasis from Renal Cell Carcinoma: A Rare Case Report.

Background: Renal cell carcinoma (RCC) frequently presents with metastatic spread, sometimes many years after treatment. However, masseter muscle metastasis is extremely rare, with just six reported cases in literature, and none in the United Kingdom (UK). Given its rarity, we hope our case will add to the body of knowledge on the subject and encourage clinicians to maintain a high index of suspicion when reviewing patients with previous RCC and an unexplained mass.

Case summary: Here presented is a 62-year-old man who previously underwent left radical nephrectomy in 2014 for an 11 cm clear cell renal carcinoma (ccRCC). He had subsequent right adrenalectomy in 2020 for a 19 mm recurrence, which was excised with clear margins. He then presented in 2022 with a three-month history of enlarging painless mass in the left side of his face. Imaging was inconclusive, but biopsy showed a singular ccRCC metastatic deposit in the masseter. Surgical resection was not possible due to extension into the infratemporal fossa, and he was referred for radiotherapy.

Conclusions: Masseter muscle, whilst rare, can be a site of distant metastases for renal cell carcinoma. Diagnosis relies on a high index of clinical suspicion in patients with prior RCC, combined with cross-sectional imaging and biopsy. Early detection gives the best chance for cure with metastasectomy.