Rosetta Genomics has published a study describing the development and initial validation of its miRview Kidney test, a 24-microRNA array-based assay that classifies a patient's primary kidney tumor into one of four main subtypes.
The paper has been accepted for publication in an upcoming issue of Molecular Oncology, and is now available from the journal as a pre-press draft online.
Robert Wassman, Rosetta's chief medical officer, said that the company has just recently made a final submission to its local Medicare contractor for miRview Kidney. "This evidence being published is hopefully very supportive of that application," he told Gene Silencing News. "And we are waiting to hear from them on that local coverage decision now."
Yael Spector, the study's lead author, told GSN this week that the paper demonstrates that the test has "very good performance," with "95 percent accuracy for the 92 percent of the samples that the test was able to return results for."
In the study, Spector and her coauthors describe how their Rosetta team developed and validated miRview Kidney using a discovery cohort of 181 patient samples to develop and train the 24-miRNA assay, and another 201 independent, blinded samples to validate the test.
According to the study authors, the group started by measuring expression levels of more than 700 known miRNAs and about 260 predicted miRNA sequences using custom Agilent arrays in 181 patient samples with known subtypes based on standard pathological diagnostic techniques.
The researchers found that 22 miRNAs were differentially expressed in at least one of the subtypes. In order to improve the panel, the group added additional miRNAs in a stepwise fashion, testing the classifier after each addition. This yielded a 25-miRNA set.
Then the team tested the classifier to see if removal of any one of the 15 miRNAs changed its effectiveness in the training sample set. One miRNA, miR-125b-5p, could be removed with no effect, leaving a final set of 24 markers.
According to the study, the group then went on to test this final panel, the backbone of miRview Kidney, on a blinded validation sample set including a balanced number of samples from each of the four cancer subtypes. The authors reported that one sample could not be assayed due to insufficient RNA. Another 16 samples were testable, but did not result in a classification into any one of the four subtypes.
For the remaining 184 samples — 92 percent of the original set — miRview Kidney classified 174, or 95 percent, accurately compared to the reference diagnosis.
The researchers also used 38 samples to evaluate the assay's inter-laboratory reproducibility between the company's two labs in Israel and Philadelphia. According to the authors, one sample could not be tested in both of the labs, and another could not be tested in just one, while two more cases resulted in no classification in either lab. For all the remaining 35 samples, both labs got the same classification result — showing 100 percent inter-laboratory concordance.
Wassman said that Rosetta sees itself as being a little "ahead of the curve" with miRview Kidney, in that the field is only just now seeing the first targeted drugs emerge with significant efficacy in renal cell cancer — historically a very poorly responsive disease, he said.
Studies of these new targeted drugs are now begging to show evidence that it makes a difference in patient response to know specifically what the tumor cell subtype is, suggesting that moving forward, there will be greater need for accurate tools like miRview Kidney, to measure these differences.
"Additionally, on the clinical side," Wassman said, "there is a trend toward more samples being taken in biopsy format where pathology [is of lower standards] than for resections. For these smaller samples, pathological subtyping can be hard or impossible, necessitating a molecular approach.
He added that Rosetta is still early in the process — although the test has been available for some time — of promoting miRview Kidney to the oncology community. "We wanted to have this article come out in press before making a major effort to move the test forward commercially — and hopefully have the Medicare coverage coming as well," he said.