Bonnie Choy

Introduction: Sarcomatoid differentiation has been reported in approximately 8% of chromophobe renal cell carcinoma (RCC) and is associated with a worse prognosis. We aim to describe the clinicopathologic and molecular findings of chromophobe RCC with sarcomatoid differentiation. Methods: Surgical pathology database was searched to identify chromophobe RCC with sarcomatoid differentiation from January 2015 to December 2021. Results: Five patients were diagnosed with chromophobe RCC with sarcomatoid differentiation. The median age at the time of diagnosis was 57 years (range 51-61 years). Three patients died after median follow-up of 12.1 months (range 1.6-18.2 months). The median tumor size was 10.7 cm (range 5.6-13.6 cm). The median percentage of sarcomatoid component was 60% (range 10-90%), and the median percentage of necrosis was 30% (range 10-50%). One tumor demonstrated osteoid formation. PAX8, keratin 7, KIT (CD117), and Hale colloidal iron were positive in the epithelial component, whereas the sarcomatoid component was positive for vimentin, CD10, and high Ki67 proliferative index. Molecular testing was performed in three specimens: all were TP53 mutated and microsatellite stable. One aggressive tumor had RB1 frameshift mutation and copy number gains for TERT and CUL4A. Conclusion: Chromophobe RCC with sarcomatoid differentiation is a rare entity with aggressive behavior. Percentage of sarcomatoid component, necrosis, and the occurrence of metastasis is associated with worse prognosis. Molecular profiling reveals frequent TP53 mutation. While TERT promoter mutation has no prognostic implication, FLCN inactivation may be associated with a less aggressive course. The clinical significance of RB1 loss is unclear.

The frequency of detection of renal masses has increased over recent decades, causing a concurrent increase in early intervention by surgery. Growing recognition that this approach was contributing to overtreatment led to the broader use of preoperative renal mass biopsy (RMB) by core biopsy and/or fine‐needle aspiration. Because more options for management, such as active surveillance and personalized therapy, are becoming increasingly available, a diagnosis by RMB is becoming a valuable tool for risk stratification and clinical decision making. Guidelines from various professional organizations have outlined situations in which RMB should be used, and it has been shown to be safe and effective. Rapid on‐site evaluation (ROSE) using touch preparations of core biopsy or fine‐needle aspiration smears provides an immediate assessment of adequacy and appropriate triage. ROSE also ensures sufficient material to perform immunohistochemistry and molecular studies for more accurate characterization of renal masses and personalized treatment. The integral role of cytopathology laboratories in precision medicine can also be successfully used in optimizing the workup of RMB from ROSE to final diagnosis, prognostication, and personalized management of kidney tumors. Herein, the authors review their extensive experience working together with interventional radiology and urology colleagues to use core biopsy and ROSE at the time of RMB for diagnosis and management of these lesions.