ORLANDO – In the largest assessment to date of circulating tumor DNA (ctDNA) in patients with metastatic renal cell carcinoma (mRCC), the majority of patients were found to have clinically relevant genomic alterations.
The most frequently occurring alterations for the entire cohort were TP53, VHL, NF1, EGFR, and ARID1A, but, importantly, the genetic profiles differed between patients receiving first-line therapy and those receiving second-line treatments.
“Compared to patients receiving first-line therapy, patients receiving post–first-line agents had increased genomic alterations in TP53, NF1, EGFR, and PIK3CA,” said lead study author Sumanta K. Pal, MD, a urologic oncologist at City of Hope, Duarte, Calif.
“These alterations underscore potential mechanisms of resistance,” said Dr. Pal, who presented the findings of his study in a press briefing held at the 2017 Genitourinary Cancers Symposium sponsored by the American Society of Clinical Oncology, ASTRO, and the Society of Urologic Oncology..
Several targeted therapies have been approved for mRCC, including vascular endothelial growth factor–targeted therapies, mammalian target of rapamycin inhibitors, and checkpoint inhibitors. However, treatment of mRCC is generally distinctly different for the first- and second-line settings.
Dr. Pal noted that, while “efforts such as the TCGA [The Cancer Genome Atlas] have shed some light on the tumor biology, it is important to keep in mind that these datasets reflect earlier stages of disease. Certainly, there may be an evolution of tumor biology as patients progress toward metastasis.”
Circulating tumor markers represent a practical means of serially assessing tumor biology, and ctDNA can account for tumor heterogeneity. In this study, the authors sought to determine the mutational landscape of mRCC as well as to assess changes across patients receiving first-line and subsequent therapies by using ctDNA.
Data were obtained from 224 patients who received ctDNA profiling at progression as part of routine clinical care using Guardant360, a CLIA-certified comprehensive plasma assay that evaluated 70 genes. Of this group, 64 and 56 patients were coded as receiving frontline and post–first-line agents, respectively.
Genomic alterations were pooled for the entire group, and first and second (subsequent) therapies were compared, based on conventional practice patterns (first-line regimens included sunitinib, pazopanib and bevacizumab, and second line included everolimus, axitinib, cabozantinib, and nivolumab).
Genomic alterations were found in 78.6% of patients, with an average of 3.3 genomic alterations per patient. For patients receiving first-line therapy, the average number of ctDNA alterations was 2.9, compared with 3.7 for those in the cohort who were receiving second-line therapy. The median (range) ctDNA variant allele fractions were 0.23 (0.05-9.92) in the first-line group and 0.24 (0.04-47.14) in second line.
The authors observed that there were disparities in genomic alterations between both patient cohorts, with the highest disparity seen in (second vs. first line) TP53 (49% vs. 25%), VHL (29% vs. 25%), NF1 (20% vs. 15%), EGFR (17% vs. 21%), and PIK3CA (17% vs. 8%).
“These alterations underscore potential mechanisms of resistance,” said Dr. Pal.
He also pointed out that there were significant differences between the current dataset and other published reports, which may reflect the advanced state of the disease of the patients in this study.
Efforts are also ongoing to add detailed data on demographics and clinical outcomes to the current dataset, Dr. Pal added.
Acting as the paper’s discussant, Primo N. Lara Jr., MD, of the University of California, Davis, Comprehensive Cancer Center pointed out that as there are no validated biomarkers of drug resistance or tumor evolution and that liquid biopsy offers a potential platform.
The use of ctDNA is a “convenient technology that offers new means to assess RCC biology,” said Dr. Lara, but the caveat is that it is “still in its infancy and has no immediate clinical application.”
The current study is “hypothesis generating only.” ctDNA changes need to be related to outcome following treatment, and the functional role of genomic alterations in RCC biology must be validated, he said.