FDA Labels xT CDx as a Breakthrough Device for Solid Tumors


An investigational HLA-LOH assay, xT CDx, now has the FDA's attention.

  • FDA breakthrough device designations are intended to put forth devices that provide more effective diagnosis or treatment of serious conditions or diseases, according to the FDA.

  • With a breakthrough device designation, the development, clinical trials, and data review for xT CDx assay will be accelerated.

  • The xT CDx assay is a single site next generation sequencing (NGS) assay that can detect alterations in 648 genes.

The FDA has granted breakthrough device designation to an HLA-LOH assay, xT CDx assay, as a companion diagnostic for use in patients with solid tumors. The assay can identify patients who may benefit from certain targeted therapies.1

HLA-LOH uses NGS and recognizes allele-specific loss of heterozygosity (LOH) for specific human leukocyte antigen (HLA) class I alleles in patients. Research shows that HLA-LOH is seen in 40% of non–small-cell lung cancers (NSCLCs).1,2 HLA-LOH loss can lead to high sub clonal neoantigen burden, APOBEC-mediated mutagenesis, upregulation of cytolytic activity, and PD-L1 positivity, according to McGranahan, et al.2

“HLA-LOH provides a clear molecular distinction between cancer and non-cancer cells and is a potential biomarker for immune therapy resistance. The Tempus HLA-LOH test is intended to measure this biomarker and better understand which patients may respond to new therapies,” said Kate Sasser, PhD, chief scientific officer of Tempus, in a press release.

Colored Genetic Code DNA Molecule Structure | Image Credit: © ktsdesign - www.stock.adobe.com

Gene code | Image Credit: © ktsdesign - www.stock.adobe.com

Currently, the xT CDx assay has FDA indications as a CDx for cetuximab (Erbitux) and panitumumab (Vectibix) to identify KRAS wild type in patients with colorectal cancer. However, according to Tempus, the assay can capture information from about 648 cancer-related genes. The assay targets more than 500 times the average coverage of tumor samples.3

“This breakthrough device designation from the FDA recognizes the novelty and potential clinical impact of our HLA-LOH test for this promising biomarker. HLA-LOH is of special interest for the application of cell therapy to treat solid tumors, but also has broader potential for other precision medicine approaches in oncology, including in combination with other established biomarkers. The Tempus test is being developed to identify HLA-LOH and may help optimize existing therapies and facilitate the advancement and implementation of novel and transformative treatments,” said Sasser.


1. FDA grants breakthrough device designation to Tempus’ HLA-LOH companion diagnostic test. News release. August 15, 2023. Accessed August 15, 2023. https://www.tempus.com/news/fda-grants-breakthrough-device-designation-to-tempus-hla-loh-companion-diagnostic-test/

2. McGranahan N, Rosenthal R, Hiley CT, et al. Allele-specific hla loss and immune escape in lung cancer evolution. Cell. 2017;171(6):1259-1271. doi: 10.1016/j.cell.2017.10.001.

3. xTCDx Technicalinformation. Tempus. Accessed August 15, 2023. https://www.tempus.com/wp-content/uploads/2023/05/Tempus-xT-CDx_Technical-Information.pdf

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