Earlier, the Fuhrman system was largely used, and was similarly based on nuclear features. Treatment
First-line treatment for metastatic PRCC has not been standardized. Thus, similar treatment approaches for clear cell RCC have been used for PRCC, even though it has a distinct tumor histology. Surgery
Nephrectomy or nephron-sharing partial nephrectomy is widely recommended to reduce the risk of metastasis by eliminating all or part of the kidney. Surgery procedures for PRCC depend on the patients status and are very similar to procedures performed on RCC patients. Targeted Therapy
Several medications that target molecular pathways in RCC have been possible options for advanced and metastatic PRCC. Among different medications, tyrosine kinase inhibitors (TKIs) and mammalian target of rapamycin (mTOR) inhibitors are effective in inhibiting angiogenesis, blocking growth and suppressing spread of the tumor. Sunitinib, sorafenib, and axitinib are TKIs with anti-vascular endothelial growth factor (VEGF), which inhibit cellular signaling by targeting multiple receptor tyrosine kinase. Everolimus and temsirolimus are used in deregulating the mTOR pathway. Specifically, mTOR inhibitors have crucial roles in regulating cell growth, cell proliferation and metabolism of highly active tumor cells. Other targeted agents such as MET inhibitors, epidermal growth factor receptor (EGFR) inhibitors, and monoclonal antibodies, are also promising treatment approaches for PRCC. Foretinib is one example of a multikinase inhibitor targeting c-MET. Considering that MET gene mutation is one oncogenic pathway of PRCC, MET inhibitors like tivantinib and volitinib are currently being investigated as a new targeted therapy option.
Typically, PRCC tends to appear homogeneous while clear cell RCC is likely to be in a heterogeneous form when the tumor is less than 3 cm in diameter. Comparatively, in cases of tumors larger than 3 cm in diameter, PRCC is generally heterogeneous with areas of necrosis and hemorrhage compared to chromophobe RCC. Solid, small PRCC tumors (<3 cm in diameter) are more easily viewed on nephrographic, excretory phase images rather than on unenhanced, corticomedullary phase images. Magnetic resonance imaging (MRI)
Magnetic resonance imaging (MRI) is recommended instead of CT for patients with an allergy to iodinated contrast materials. As some renal tumors do not enhance significantly on CT, MRI examination is required to be performed with more sensitive contrast enhancement. On MRI, the distinct features of PRCC are fibrous capsules and homogeneously low single intensity on both T1- and T2-weighted images. Specifically, PRCC exhibits hypointensity due to its dense collagenous matrix or deposition of calcium and hemosiderin within the tumor. Such visual features help PRCC to be differentiated from clear cell RCC, which has heterogeneously higher single intensity shown on T2-weighted images. PRCC displays the smallest tumor-to-cortex enhancement at corticomedullary and nephrographic phases when juxtaposed with clear cell and chromophobe RCCs. Grading System
The WHO/ISUP system is histological tumor grading system for renal cell carcinoma, suggested by the International Society of Urologic Pathologists (ISUP) in 2012 to diagnose tumor grades based on nucleolar prominence. Currently recommended by the WHO, this four-tiered WHO/ISUP grading system has also been validated for PRCC.