Renal Involvement in Cases of Spindle Epithelial Tumor with Thymus-Like Differentiation : A Case Report and Review of the Literature

Abstract

Background: Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a very rare neoplasm of the thyroid first described by Chan and Rosai in 1991. Renal involvement usually occurs as part of a disseminated metastatic picture. SETTLE is believed to arise from branchial pouch or thymic remnants and shows primitive thymic differentiation. Presentation: A 41-year-old male presented with a thyroid mass in 2005. The patient underwent a total thyroidectomy followed by radiation therapy. Pathology concluded papillary thyroid cancer. In 2011, the patient was admitted with worsening cough. CT showed lung involvement, multiple mediastinal lymph nodes, and a left renal mass. A biopsy established the diagnosis of SETTLE. Four cycles of platinum chemotherapy were given. In 2014, the patient was referred to Urology with progressive flank pain and hematuria. CT showed a progression of the renal mass, and results of an U/S guided biopsy of the kidney were consistent with SETTLE. An elective radical nephrectomy was performed in late 2016 to relieve symptoms. The patient is currently being followed as an outpatient. Conclusion: Due to the rare nature of SETTLE, algorithms for the diagnosis, treatment, and outcomes are not established. Although SETTLE presents as a low-grade malignancy, this case, as well as other reported cases with a long follow-up duration, suggested that it can metastasize many years after initial diagnosis. More data is needed to elucidate the risk and prognosis of renal metastasis in SETTLE.