ASCO GU 2018: Best of Journals: Renal Cell Carcinoma - Radiology

San Francisco, CA ( Dr. Davenport delivered an overview of the most impactful radiology literature related to renal cell carcinoma (RCC) in 2017. Much of the literature focused on trying to better characterize renal lesions to better conclude if a renal mass is benign or malignant. The literature also discussed attempts at using imaging modalities to predict tumor pathology, an attempt which is making significant headway.

Herts et al. published a flowchart for working up an incidental renal mass on non-contrasted and contrasted CT scans. In brief, the flowchart indicates that are tumors too small to characterize and are homogeneous are likely benign; and it is probably safe to forgo further follow-up. >=70HU masses are likely hemorrhagic or proteinaceous and benign. Heterogeneous masses with thick or irregular walls require further workup. Post-contrast, homogeneous masses that enhance >20HU need further workup. 

Enhancement on CT is defined as +20HU after contrast injection. A <20HU change likely indicates a cyst. Given the starting HU of pre-contrast cysts, a post-contrast lesion with 21-39HU is considered to likely be a benign cyst. Post-contrast attenuation is probably not reliable for small masses <1.5cm, which is especially true for endophytic masses. Papillary masses are also not well characterized by CT contrast enhancement. 

Davenport et al. published on CT “reporting characteristics” for renal masses and the preferences for reporting structure by various specialties. Essential components of a CT report include comparing the scan to previous imaging and staging cysts, especially Bosniak III and up. Further anatomic characterization of the mass is somewhat based on preference. This ranges from adding a nephrometry score to discussing management options for Bosniak IIF cysts. More work is needed to better characterize the most important components of radiology reports that will satisfy all specialties involved in the management of these lesions. 

Chandrasekar et al. looked at a large retrospective cohort evaluating the surveillance of cystic masses. Bosniak IV cysts were obviously treated more often than Bosniak II cysts. 80% of all cysts were managed non-operatively. Only 1 cancer-specific death occurred in a patient who had Von Hippel Lindau syndrome. It is important to keep several things in mind when evaluating renal cysts. The Bosniak classification system stratifies the risk of malignancy but not the risk of metastatic disease or death from RCC. In general, even if a lesion turns out to be RCC, cystic RCC is more indolent than solid RCC. Lastly, the natural history of Bosniak IIF and III cystic lesions supports the use of active surveillance as an initial management strategy.

Canvasser et al. evaluated the accuracy of MRI to predict renal mass pathology. They developed an algorithm that aimed to characterized lesions likely to represent clear cell RCC (ccRCC). Seven blinded radiologists used this algorithm to attempt to predict if a renal lesion represented ccRCC. The test characteristics were quite impressive – they report an AUC of 0.82 to 0.92 for properly diagnosing ccRCC. 

Dr. Davenport summarized the take-home points from the reviewed literature. Small (too small to characterize), incidental, homogeneous renal lesions are likely benign. They should probably be reported but do not need clinical follow-up. Heterogeneous/intermediate attenuation incidental masses need further work-up. Radiology standards currently do prescribe minimal reporting requirements, and robust template-based reporting will likely be more universal in the near future.  The more we learn about cystic masses, the more we are confident that many can be managed conservatively, and Bosniak III cystic masses can reasonably be placed on active surveillance for initial management. 

Finally, MRI algorithms may help predict pathology as we become more familiar with the imaging characteristics of different masses. The results of such efforts are interesting, and have many intriguing implications for the future of how we manage patients diagnosed with incidental renal lesions. However, this science is still in its infancy and should not be used in clinical practice without extreme caution.

The identification of incidental small renal lesions continues to rise, and characterizing these lesions with noninvasive, radiological modalities is becoming increasingly valuable. Hopefully, our evolving understanding of renal mass imaging will lead to more appropriate therapies and management strategies for these patients in the future. 

Presented by: Matthew Davenport, MD, University of Michigan Comprehensive Cancer Center

Written by: Shreyas Joshi, MD, Fox Chase Cancer Center, Philadelphia, PA at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA