ASCO GU 2017: Imaging as Biomarker of Response in Advanced Renal Cell Carcinoma

Orlando, Florida USA (UroToday.com) Dr. Andrew D. Smith reported that a key challenge in the care of patients with metastatic renal cell carcinoma (RCC) is the assessment of tumor response following therapy. An ideal imaging biomarker would need to capture the therapy’s primary effect, have a simple objective metric, require being widely available and easy to perform on any scanner, seem applicable across a broad range of image-acquisition parameters, and be suitable for longitudinal tumor response assessment. Dr. Smith presented key imaging biomarkers to assess response in advanced RCC.
Changes in tumor size after chemotherapy remain the standard of care for assessing and reporting tumor response. Size is said to offer a variety of advantages: single-dimension length is sufficient for metastatic evaluation and is highly reproducible, tumor length is highly resistant to computed tomography (CT) or magnetic resonance imaging or MRI image-acquisition techniques, and zero length equals no tumor. Currently, size is the best quantitative imaging tumor response metric, and other tumor metrics should be considered when size is not informative. Size can also be modified to focus on other components of interest, such as vascular tumor burden. With contrasted imaging, the amount of vascular tumor can be measured as an absolute or percentage change with good interobserver agreement.

CT attenuation can also be used as an imaging biomarker more specifically designed to assess the degree of necrosis posttherapy. Change in attenuation can be measured and absolute changes compared with good interobserver reliability. There are several limitations associated with CT attenuation, the most important being the need for contrast in each scan, as scans with and without contrast cannot be compared. Attenuation is also affected by contrast injection and several patient factors that make direct comparison between scans quite challenging.

In addition, Dr. Smith noted that CT texture can be used to follow tumor changes during therapy. That texture is what allows us to measure alterations in tumor heterogeneity. Texture can be quantified with computer modeling, which will allow for more objective measurements. There is no extra expense associated with the acquisition of the data, and the dimensions are made with the available imaging data output. As with CT attenuation, there are several limitations associated with imaging acquisition and changes in patient factors.

With regard to imaging criteria used to observe tumor response, the most validated have been the RECIST criteria, which work very well for longitudinal follow-up of tumor changes, but they lack predictive ability. If prediction of response is needed, a better imaging guideline to use would be either the vascular tumor burden criteria or 10% tumor-diameter shrinkage criteria.

The follow-up of tumor burden with immune checkpoint inhibitors has some key pattern differences seen in targeted therapy. The most important phenomenon to know about is pseudoprogression. It is not uncommon to see tumor growth with immunotherapy that regresses with time. On imaging criteria Dr. Smith favored the use immune-related RECIST (IrRECIST).

In conclusion, he predicted that the future of metastatic RCC response evaluation will be likely be in the form of Computer-Assisted Response Evaluation or CARE platforms, which have the potential to prevent common errors in tumor response assessment, simultaneously evaluate tumor response by multiple criteria, standardize reporting, and enhance communication between the radiologist, the treating clinicians, and the patients.

Presenter: Andrew D. Smith, MD, PhD, University of Mississippi Medical Center

Written By: Andres F. Correa, MD, Society of Urologic Oncology Fellow, Fox Chase Cancer Center

at the 2017 Genitourinary Cancers Symposium - February 16 - 18, 2017 – Orlando, Florida USA

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