Three commercially available diagnostic tests were similarly effective in measuring PD-L1 protein expression on non-small cell lung cancer (NSCLC) tumour samples, indicating that health care providers may someday be able to use these tests interchangeably when determining which patients will respond best to anti-PD-L1/PD-1 immunotherapeutic drugs, according to research presented at the AACR Annual Meeting 2016.

“PD-L1-directed antibodies are emerging as effective therapeutics in monotherapy and in combination in multiple oncology settings,” said the study’s lead author, Marianne Ratcliffe, MA, PhD, diagnostic associate director at AstraZeneca.

An interview with Dr Ratcliffe can be viewed here.

She explained that several different diagnostic tests, or assays, are effective in determining which patients’ tumours express high levels of PD-L1 and might, therefore, respond best to targeted treatment.

“Before our study, we did not know whether the different assays identified the same patients,” Ratcliffe said, adding that the tests were developed on different platforms and use different antibody clones and testing protocols.

“Clearly, for the oncology community, this presents a number of issues, including a lack of confidence in being able to identify appropriate patients for treatment with these targeted therapies,” Ratcliffe said. “Our current study complements the ongoing Blueprint initiative, which is also tackling the issue of PD-L1 assay harmonization.”

This study compared the Ventana SP263 assay, developed by Ventana in collaboration with AstraZeneca for use in evaluating patients for the immunotherapeutic drug durvalumab, an anti- PD-L1; the Dako 22C3 assay, made by Dako and approved for the U.S. Food and Drug Administration (FDA) as a companion diagnostic to identify patients for pembrolizumab (Keytruda), an anti-PD-1; and the Dako 28-8 assay, made by Dako and approved by the FDA as a complementary diagnostic for nivolumab (Opdivo), an anti-PD-1.

All three tests assess the percentage of tumour cells whose membranes stain positive for the PD- L1 protein.

A cut-off point is set for each test, and patients whose tumours score above the cut-off point are determined to be more likely to respond to the corresponding therapy, Ratcliffe explained.

In this study, the largest to date, approximately 500 tumour biopsy samples from patients with NSCLC were assessed because all three tests have been previously validated for that disease.

The study determined that the patient population defined by Ventana SP263 at the 25 percent cutoff point is similar to the group identified by the Dako 28-8 at the 10 percent cutoff.

The study also showed a high degree of concordance between the SP263 and 22C3 assays if a 50 percent cutoff point was applied in both cases.

Ratcliffe said that the three tests achieved overall percentage agreement of more than 90 percent.

The results also indicate which cutoff points should be used to optimise agreement between a positive or negative PD-L1 result, which will help the medical community to compare results from clinical studies that have used different tests.

Ratcliffe said the study results indicate that it may be possible to extrapolate the results from one test to that of another test, and could someday allow physicians to use the tests interchangeably, though she added that further research is needed to confirm the findings.

Source: AACR