Use of the 92-gene assay to identify tumor type and direct predictive biomarker testing in limited tissue specimens.

Abstract

e19072 Background: Limited tissue availability from biopsies can limit comprehensive diagnostic testing and individualized care. The 92-gene assay is a gene expression-based cancer classifier that requires a minimal number of tumor cells (~300) and may improve the efficiency of tissue usage as a molecular complement to IHC in cases with limited diagnostic material. In this study, the reporting rate and utility of molecular classification in limited tissue cytology specimens, as well as the frequency of directed predictive biomarker testing were examined. Methods: Four hundred thirty eight FFPE cytopathology cases (ie, fine needle aspirates, pleural effusions, ascites) with indeterminate diagnosis where the 92-gene assay (CancerTYPE ID, bioTheranostics Inc.) was used in clinical care were included in the analysis. The 92-gene assay reporting rate and tissue availability to perform downstream biomarker testing were analyzed. Results: The 92-gene assay provided a molecular diagnosis in 86% (n=378) of cytopathology specimens submitted for diagnostic testing. Twenty-four distinct tumor types were predicted including: 9% lung (n=41), 8% urinary bladder (n=34), 8% pancreaticobiliary (n=34), 8% ovary (n=34), 7% gastroesophageal (n=32), 5% intestine (n=20), and 1% melanoma (n=5). In 66 patients with molecular diagnoses where reflex biomarker testing was applicable (lung, CRC, melanoma), 33% of cases had additional predictive biomarker testing performed, and 2 or more biomarker tests were performed on 15% of cases. The most common tests ordered were EGFR mutations (n=16), KRAS mutations (n=8), BRAF mutation (n=8), and ALK rearrangement (n=5). Conclusions: These findings demonstrate the suitability and high reporting rate of the 92-gene assay in limited tissue cytologic specimens and successful predictive biomarker testing in appropriate cases. With the growing number of molecularly-targeted therapies requiring predictive biomarker testing, use of the 92-gene assay may have increased utility in indeterminate cancer cases where limited tissue specimens are the only option for diagnosis and treatment planning.