1. Overview
Guardant 360 CDx is a comprehensive liquid biopsy–based genomic test that analyzes circulating tumor DNA (ctDNA) shed into the bloodstream from cancer cells. As a non-invasive alternative to tissue biopsy, it provides a real-time overview of the genomic landscape of both primary and metastatic tumors.
The test uses a secure digital next-generation sequencing (NGS) platform that is reported to be up to 1000 times more accurate than standard sequencing methods, achieving extremely high specificity and minimizing false-positive results.
Guardant 360 CDx is FDA-approved for use in advanced solid tumors and delivers results in as little as 7 days, making it a rapid and clinically practical tool for precision oncology.
2. Clinical Context / Indications
The test does not address symptoms directly but is indicated in patients with advanced solid malignancies, particularly when conventional tissue biopsy is challenging or inadequate.
It is useful in the following clinical scenarios:
- When the tumor cannot be easily located
- When a tissue biopsy is difficult or unsafe
- When patients do not respond to standard chemotherapy
- When patients are being considered for targeted therapy or clinical trials
Guardant 360 CDx is applicable across a wide range of cancers, including non-small cell lung cancer (NSCLC), breast cancer, melanoma, cholangiocarcinoma, colorectal cancer, ovarian cancer, and pan-tumor indications such as NTRK1/2/3 gene fusions.
3. Technology and Genomic Coverage
Guardant 360 CDx is an NGS-based assay that sequences more than 80 cancer-related genes relevant to oncology. It detects all four major classes of genomic alterations:
- Single-nucleotide variants (SNVs)
- Insertions and deletions (Indels)
- Copy number alterations (CNAs)
- Gene fusions
In addition, the test reports microsatellite instability (MSI) status, an important biomarker for immunotherapy eligibility.
Key biomarkers detected include alterations in genes such as EGFR, KRAS, BRAF, PIK3CA, ALK, ROS1, RET, MET, ERBB2 (HER2), TP53, BRCA1, BRCA2, NRAS, IDH1, PTEN, FGFR2, FGFR3, and NTRK genes, among others. These genes encode proteins that are often directly targetable with approved therapies.
4. Sample Collection and Processing
Guardant 360 CDx requires a blood sample, with plasma preferred over serum. Serum is avoided because the clotting process releases genomic DNA from white blood cells, which can interfere with ctDNA analysis.
Approximately 3.0 mL of blood is collected in EDTA (lavender-top), citrate (blue-top), or heparin (green-top) tubes. Plasma must be separated immediately, frozen promptly, and transported without thawing until it reaches the laboratory.
Proper collection, centrifugation, and storage are essential to maintain ctDNA integrity and ensure accurate results.
5. Prognostic and Clinical Utility
Guardant 360 CDx provides actionable genomic information that helps clinicians tailor therapy based on the individual tumor profile. It identifies targetable mutations, resistance mechanisms, and molecular drivers of disease progression.
The test is described as prognostic rather than predictive, as it evaluates the likelihood of response or resistance to standard therapies based on tumor genomics, rather than predicting response to a specific experimental intervention.
Clinical applications include:
- Guiding targeted therapy selection
- Monitoring treatment response
- Identifying resistance mutations
- Tumor mutation profiling
- Monitoring disease progression
- Supporting precision oncology decision-making
- Acting as a companion diagnostic for certain targeted therapies
6. Advantages
Key advantages of Guardant 360 CDx include:
- Non-invasive testing via blood draw
- Faster results compared to tissue biopsy
- Ability to obtain a comprehensive genomic profile
- Useful when tumor tissue is inadequate or unavailable
- Enables real-time monitoring of tumor evolution
- In some cases, may detect tumor mutations more effectively than tissue biopsy, particularly in NSCLC
7. Limitations
Despite its utility, Guardant 360 CDx has several limitations:
- It is not a replacement for germline genetic testing
- Sensitivity depends on the degree of tumor DNA shedding
- Limited concordance with tissue biopsy in some cases
- A restricted number of reportable genes and variants compared to large tissue-based panels
- Potential analytical interference due to sample quality issues
- Possible influence of clonal hematopoiesis of indeterminate potential (CHIP)
- Limited indications for use in certain clinical contexts
