New ESMO Recommendations for Investigating Circulating Tumor DNA

Applications of ctDNA Analysis

In patients with cancer, a fraction of DNA from tumor cells (ctDNA) can be found in blood plasma and carries a wealth of information about its origin. Current recommendations from the ESMO expert panel state that the strongest evidence for routine clinical use of ctDNA analysis is with polymerase chain reaction (PCR) techniques or next-generation sequencing (NGS) for profiling molecular pathologies of advanced solid tumors such as those of the lung, colon, stomach, or breast.

Conversely, there is still a lack of sufficient evidence for the use of ctDNA testing for ongoing monitoring of cancer during treatment, early relapse estimation, or screening asymptomatic individuals. Although clinical validity has been established in many cases, proof of actual clinical benefit is lacking. For instance, it is well documented that the presence of ctDNA in plasma after curative treatment for early-stage cancer is associated with a high risk of future relapse. However, it is not yet known how clinical outcomes would change if physicians were to therapeutically respond to this finding. Further research is needed in such cases.

Genetic Profiling Using ctDNA in NSCLC

For patients with non-small cell lung cancer (NSCLC) who have not yet started treatment, the standard practice is to test tumor tissue for a panel of molecular pathologies—mutations in genes like EGFR, ALK, MET, ROS1, among others. The ESMO expert panel has assessed that ctDNA analysis can be an alternative when rapid results are needed and tissue biopsy would significantly delay treatment decisions, when a tissue biopsy is not feasible, or in cases of bone lesions that are difficult to process. However, the method also has its limitations. For instance, small intrathoracic tumors or intracranial lesions do not release much ctDNA, leading to a high rate of false negatives. ctDNA analysis also has reduced sensitivity for detecting gene fusions.

In patients undergoing NSCLC treatment with tyrosine kinase inhibitors (TKIs), resistance to treatment often develops. In the case of anti-EGFR TKIs, this is frequently due to acquiring the T790M mutation in the EGFR gene. If this mutation is identified, targeted drugs that are not affected by the mutation can be indicated. Currently, it is well established to test ctDNA using NGS, and only if the result is negative is the absence of the mutation confirmed with tissue testing. Similar protocols exist for testing ctDNA using NGS for other EGFR mutations, as well as for ALK and ROS1 positive NSCLC. Evidence is still lacking to confirm that ctDNA testing is also suitable for detecting MET gene amplification, another resistance mechanism to TKIs. ctDNA analysis has lower sensitivity for detecting deletions and amplifications. Additionally, ctDNA does not reliably indicate a change in differentiation to squamous or neuroendocrine histological types.

Challenges in ctDNA Testing

One significant issue with ctDNA testing is the occurrence of false negative results, where the test fails to detect a molecular pathology despite its presence in the tumor. This can be due to technical and pre-analytical factors, such as low levels of ctDNA in the sample or low test sensitivity, as well as biological factors if the tumor does not release ctDNA as expected.

False positive results also occur. Detection of a molecular pathology that is unrelated to the cancer can result from the accumulation of mutations in hematopoietic cells, whose DNA is abundantly present in plasma after apoptosis. Therefore, the ESMO panel recommends concurrent testing of leukocyte DNA profiles.

Lastly, the substantial costs associated with ctDNA testing and the possibility of coverage by healthcare payers cannot be overlooked.

Conclusion

The universal ctDNA analysis, serving purposes from screening to treatment selection and efficacy evaluation to relapse risk assessment, is likely a fiction. For each clinical question, the most appropriate test must be sought, one that robustly demonstrates its clinical and analytical validity and clinical utility. In most cases, this evidence is still being gradually collected. However, as illustrated by the example of genetic profiling of advanced solid tumors, ctDNA may soon become a viable alternative at least in situations where standard procedures cannot be followed.

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Source: Pascual J., Attard G., Bidard F.-C. et al. ESMO recommendations on the use of circulating tumour DNA assays for patients with cancer: a report from the ESMO Precision Medicine Working Group. Ann Oncol 2022 Aug; 33 (8): 750−768, doi: 10.1016/j.annonc.2022.05.520.