Building a Better Molecular Mouse Trap: Circulating Tumor DNA Detects Resistance Mutations in Lung Cancer

Hatim Husain, MD

Hatim Husain, MD

About the Study

Few areas of oncology have seen a more robust use of targeted therapies than lung cancer. The availability of mutation-specific treatments, an expanding knowledge of key oncogenic drivers, and an increasing understanding of potential resistance mechanisms have provided immense opportunities for research and development of new therapies.^1-5Central to this research, however, is a need for rapid and reliable strategies for mutational assessment, not only for the initial tumor biopsy, but also throughout the course of treatment. Data presented at the European Lung Cancer Conference (ELCC) detailed a new method for mutational assessment in lung cancer that offers the possibility for dynamic, ongoing evaluation of tumor cell genetics, in a safe and noninvasive manner.⁶Resistance mutations such as the epidermal growth factor receptor(EGFR) T790Mvariant are known to be the harbingers of progressive disease in patients with metastatic non—small cell lung cancer (NSCLC), andT790Min particular is known to confer resistance to EGFR-targeted therapies such as erlotinib and gefitinib.^1-5Multiple third-generation anti-EGFR drugs forEGFR T790M-mutation—positive disease are in clinical development.^1-3The use of noninvasive, nontissue-based approaches for detecting resistance mutations such asT790Mwould therefore be highly desirable for treatment.⁶

The study presented at ELCC had 3 main objectives. The first was to assess the feasibility of detectingT790Min urinary circulating tumor DNA (ctDNA) compared with the current gold standard of tissue biopsy. A second objective was to test for this mutation in patients undergoing treatment with first-line anti-EGFR tyrosine kinase inhibitors. A third objective was to assess the pharmacodynamics of early response in the first week to second-line anti-EGFR agents via daily, and then subsequently weekly, monitoring for EGFR mutations in urine specimens.

A Need for Ongoing Mutational Assessment

Results of the study showed thatT790Mcould be detected in 15 of 22 patients (68%) who were receiving anti-EGFR therapy. Patients with tissue-detectedT790Malso had positive urine samples. Furthermore, patients with clinically suspectedT790M, who were either negative in tissue biopsy or lacking any biopsy findings, could be identified with urine testing.T790Mcould be detected as early as 3 months, 3 weeks prior to radiologically detected progression in patients receiving erlotinib. Early pharmacodynamic events, occurring within hours or days of anti-EGFR treatment, are being studied using ctDNA to identify anti-EGFR responders much faster than would ordinarily be possible with follow-up computed tomography (CT) scans.  Hatim Husain, MD, is an assistant professor of hematology-oncology at the Moores Cancer Center at the University of California, San Diego, and first author on this proffered paper, which presented at the 5th ELCC (April 15-18, 2015) in Geneva, Switzerland.⁶

“I am interested in understanding how biomarkers, and specifically ctDNA, may be used to inform clinical decision making. I think lung cancer is a great model to look at this, because we know many of the targetable oncogenic drivers that are important in the disease,” Husain said. Husain added that he recognizes the potential benefit of ongoing mutational assessments.

A Useful and Abundant Assessment Source

Implications for Treatment

An Ongoing Industry-Academia Collaboration

“Tumors are not static. They are continuously evolving and changing. Systems and methodologies that can less invasively capture how the biology of the cancer is changing, in my opinion, may have the potential to inform clinical decision making,” Husain said.The study detailed the use of ctDNA obtained from patients’ urine samples to evaluate tumor genetics in patients with metastatic NSCLC treated with erlotinib who were confirmed through tissue biopsy to have theT790Mmutation.⁶The results demonstrated that an average of 0.4 µg of ctDNA can be detected in patients’ urine samples, and that mutations such asT790Mcould be identified, with a lower limit of detection of 2 copies in a background of 60 ng wild-type DNA, with an analytical sensitivity of 0.01%.⁶The study reports a concordance sensitivity of 100% between tissue and urine. In patients who were initially negative in the tissue, theT790Mmutation could be detected in the urine and, on repeat biopsy, the urine findings were confirmed.Early detection of resistance mutations may also serve to guide clinicians to other targeted therapies when the one currently in use is no longer effective. “We have inhibitors that are specific againstT790M, and when patients develop the mutation and are treated with specific inhibitors, we see a marked decline in theT790Mpopulation,” Husain said. “We can understand the kinetics of the tumor in real time, in a way that radiography could not demonstrate. Radiology gives us ideas about anatomic structure and size, but not necessarily the qualitative assessment of the tumor.”The study represents a collaborative effort between the UCSD Moores Cancer Center and Trovagene In., the developer of the testing method in urine. Husain views the effort as important, noting that, “The best way to treat cancer is with the right drug, but equally important is the right way to detect who the drug should be used for. This is really important for drug development [and for] clinical practice, because we can get an appropriate readout on how the tumor is changing in real time and hopefully can understand how the drugs are working.”

Vlada Melnikova, MD, PhD, vice president of research and development at Trovagene, shares this goal. “With this lung cancer study, we continue to expand our urinary cell-free DNA platform for quantitative detection and monitoring of actionable cancer mutations. As a completely noninvasive specimen, urine enables frequent collections, and we are now showing how this accessibility can be applied to monitoring immediate early effects of targeted therapies,” Melnikova said.

References

1. Aggarwal C. Targeted therapy for lung cancer: present and future.Ann Palliat Med. 2014; 3(3):229-235.
2. Stasi I, Cappuzzo F. Second generation tyrosine kinase inhibitors for the treatment of metastatic non-small-cell lung cancer.Transl Respir Med. 2014; 2:2.
3. Stewart EL, Tan SZ, Liu G, Tsao MS. Known and putative mechanisms of resistance to EGFR targeted therapies in NSCLC patients with EGFR mutations—a review.Transl Lung Cancer Res. 2015;4(1):67-81.
4. Yun CH, Mengwasser KE, Toms AV, et al. The T790M mutation in EGFR kinase causes drug resistance by increasing the affinity for ATP.Proc Natl Acad Sci U S A. 2008;105(6):2070-2075.
5. Shih JY, Gow CH, Yang PC. EGFR mutation conferring primary resistance to gefitinib in non-small-cell lung cancer.N Engl J Med. 2005;353(2):207-208.
6. Husain H, Kosco K, Guerrero S, et al. Detection of EGFR T790M Mutation in Urinary Circulating Tumor DNA from Metastatic Non-Small Cell Lung Cancer Patients. Abstract accepted for Proffered Paper (Oral) presentation during the 5th European Lung Cancer Conference (ELCC), April 15-18, 2015, Geneva, Switzerland.