Use of circulating tumour DNA in nasopharyngeal carcinoma to detect minimal residual disease
- 1 Internal Medicine, Beaumont Health, Royal Oak, Michigan, USA
- 2 Hematology and Medical Oncology, Oakland University William Beaumont School of Medicine, Troy, Michigan, USA
- Correspondence to Dr Bipin Ghimire; bipin.ghimire@beaumont.org
Abstract
Circulating tumour DNA (ctDNA) is defined as short DNA sequences shed by tumour cells into the systemic circulation. A promising use of ctDNA includes the detection of minimal residual disease (MRD) and is currently being studied in multiple types of solid tumours. Literature for the use of individualised ctDNA in nasopharyngeal carcinoma (NPC) is not available, although circulating Epstein-Barr virus DNA level is validated as a prognostic factor. We present a man in his 40s diagnosed with stage IV NPC who was started on chemotherapy with cis-platinum and gemcitabine. Serial monitoring of ctDNA completed to aid in detecting MRD after treatment demonstrated initial up-trending values correlating with subsequent imaging findings showing progression. Reinitiation of a different chemotherapy regimen significantly improved the ctDNA level, with corresponding imaging exhibiting a similar response. This case provides insight into the potential use of ctDNA in NPC and the benefit of serial ctDNA monitoring during treatment.
Background
Circulating tumour DNA (ctDNA) is defined as short DNA sequences shed into the systemic circulation by tumour cells. It is a subset of a pool of circulating DNA fragments called cell-free DNA (cfDNA).1 One of the promising uses of ctDNA analysis is to detect minimal residual disease (MRD), which has proven to be a marker of disease recurrence.2 Various studies have been conducted to verify this possible utility of individualised ctDNA, mostly in solid tumours such as colon, breast, lung, pancreatic and urothelial malignancies.2 These studies have primarily focused on postoperative or post-treatment use of ctDNA for detection of recurrence and its impact on survival. In addition, detection of MRD by ctDNA analysis can be used to monitor the progression of disease or response to treatment, but studies are limited in this regard.2
Pretreatment and post-treatment cell-free Epstein-Barr virus (EBV) DNA level is a known prognostic factor in NPC, but the use of individualised ctDNA in nasopharyngeal carcinoma for the detection of recurrence, progression or response to treatment is not established in literature.3 We present a case of nasopharyngeal carcinoma in which serial monitoring of ctDNA showed corresponding changes with imaging in the event of progression as well as response to treatment.
Case presentation
A man in his 40s initially presented to his primary care physician’s clinic with progressive bilateral neck swelling, unintentional weight loss and fatigue for approximately 2–3 months. Extensive cervical lymphadenopathy was noted on physical examination. Malignancy was considered highly likely with his history of chronic smoking, and further workup was initiated.
Investigations
CT neck showed a right nasopharyngeal mass with extensive bilateral cervical and supraclavicular lymphadenopathy. A core biopsy of a cervical lymph node revealed poorly differentiated squamous cell carcinoma. Nasopharyngoscopy also affirmed the presence of a right nasopharyngeal mass. Staging Positron Emission Tomography (PET) CT demonstrated additional numerous anterior mediastinal and left hilar lymphadenopathy along with multiple pulmonary, hepatic and osseous metastases. Biopsy of the nasopharyngeal mass was not performed as the patient was diagnosed with stage IV nasopharyngeal carcinoma based on the imaging, direct visualisation and lymph node biopsy findings.
Treatment
After the diagnosis, he was started on chemotherapy with gemcitabine and cis-platinum. Next-generation sequencing revealed PDL-1 positivity; thus, pembrolizumab was added to the treatment regimen. The patient received six cycles of the chemotherapy regimen.
Outcome and follow-up
Following six cycles of the chemotherapy, a repeat CT of the neck and chest/abdomen/pelvis showed resolution of the primary lesion, pulmonary nodules and hepatic lesions with residual cervical lymphadenopathy, suggesting a favourable response to treatment. The patient was then continued on immunotherapy with pembrolizumab alone.
The patient had ctDNA testing completed during interval follow-ups, which were done using the Signatera testing method. The ctDNA levels are reported as mean tumour molecules per mL (MTM/mL), which is calculated based on the mean of ctDNA molecules detected per mL of plasma. These tests were done alongside repeat imaging to support early detection of residual disease or recurrence. The timeline is demonstrated in figure 1.
The trend of circulating tumour DNA levels with the timing of the test (postchemotherapy) and corresponding imaging.
Three months after the completion of chemotherapy, the first ctDNA testing was completed and showed a level of 23.41 MTM/mL. A repeat level 1 month later showed an up-trending value of 143.35 MTM/mL. PET CT 2 weeks after the second ctDNA test still showed resolution of primary, hepatic and pulmonary lesions but demonstrated new avid axillary/subpectoral lymphadenopathy with significant residual cervical lymphadenopathy suggesting minimal disease progression (figure 2). No changes to the treatment regimen were made at that time.
PET CT showing enlarged right axillary (new) and residual cervical avid lymphadenopathy.
ctDNA was repeated 2 months after the second test and was still up trending to 181.29 MTM/mL. The CT neck and CT chest/abdomen/pelvis 1 month later showed an interval increase in the size of the previously noted bilateral cervical, supraclavicular, axillary and upper chest wall/lower neck lymphadenopathy, along with the development of new enlarged lymph nodes (figure 3). Worsening metastatic disease was confirmed on a right supraclavicular lymph node biopsy, which showed carcinoma with squamous differentiation. At this point, the patient was restarted on chemotherapy with carboplatin, paclitaxel and pembrolizumab for disease progression. Cisplatin was not used as he had developed neuropathy with the previous regimen.
CT neck showing bilateral enlarged supraclavicular lymphadenopathy (arrow pointing to the largest lymph node).
Repeat ctDNA 1 month later, after completing one cycle of the new chemotherapy regimen, was still up trending to 888.48 MTM/mL. Following two more cycles of chemotherapy, ctDNA was again tested and showed marked improvement to 0.97 MTM/mL. Repeat imaging after a month and completion of one more cycle of chemotherapy showed complete resolution of a majority of the cervical, supraclavicular, axillary and upper chest wall lymphadenopathy with a residual but significant reduction in the size of the left jugular lymph nodes. These imaging findings and the improved ctDNA level implied a favourable response to treatment. Thus, the patient was continued on his current chemotherapy regimen, and his treatment is ongoing. He has not experienced any significant adverse effects with the new regimen.
Discussion
ctDNA analysis has a wide array of possible clinical uses, such as tumour molecular profiling, tracking therapeutic response, monitoring for development of resistance to a treatment regimen, early cancer detection and detection of post-treatment MRD.1 For the signatera ctDNA test to detect MRD, whole-exome sequencing is performed first in the patient’s tumour sample. A set of 16 the most common patient-specific mutations (single nucleotide variants or indel variants) are selected for multiplex-polymerase chain reaction (mPCR) next generation sequencing, which is used to identify these variants in the plasma. Plasma samples with ≥2 variants detected are deemed ctDNA positive.4 It is being widely studied in multiple solid tumours.
Nasopharyngeal carcinoma is commonly reported in the endemic regions, especially China and Southeast Asia, and is rare in non-endemic populations, with a reported incidence in the USA being <1 in 100 000 population.5 Pretreatment and post-treatment cell-free EBV DNA level is a validated prognostic indicator in NPC,3 and there are studies from the endemic region comparing circulating tumour cells (CTCs) with the EBV DNA levels as a prognostic factor.6 7 However, the detection of such EBV DNA is not personalised to each patients’ specific mutations as in the ctDNA test. There is currently no literature that we have identified which focuses on the use of individualised ctDNA to detect MRD in NPC.
Although not studied in NPC, Wang et al 8 demonstrated that an increasing trend of ctDNA levels in colon cancer patients was associated with a higher recurrence rate than in patients with a decreasing trend after completion of chemotherapy. In our patient, ctDNA testing demonstrated variable changes with initial up-trending levels, which correlated with corresponding imaging and biopsy showing disease progression. After initiation of a new chemotherapy regimen and completion of a few cycles, there was a significant drop in ctDNA level, which again correlated with subsequent imaging showing a favourable response to treatment. Such variability of ctDNA in a single patient and its implications have not been well described in the current literature.
This analysis and trend provide insight into the potential use of MRD detection by individualised ctDNA in nasopharyngeal carcinoma patients and the importance of serial ctDNA level monitoring as it could provide evidence for worsening disease or response to treatment even prior to imaging. Medicine is constantly looking for predictive and prognostic factors used for quick and easy verification of neoplastic process, and ctDNA could fulfil such a function. However, we cannot generalise the use of ctDNA in NPC patients with just one case. More research is needed on larger groups.
Learning points
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One of the promising uses of circulating tumour DNA (ctDNA) analysis is to detect minimal residual disease and is currently being studied in many different types of tumours.
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Our case report describes a patient with nasopharyngeal carcinoma in whom ctDNA trends were similar to findings on imaging in regards to progression followed by response to treatment. However, further studies need to be completed before we can determine if individualised ctDNA is a reliable form of monitoring progression, recurrence or response to treatment in nasopharyngeal carcinoma.
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Given the findings in our patients, another possible use of ctDNA might be to monitor for disease progression or response to ongoing treatment prior to imaging studies being completed.
Ethics statements
Patient consent for publication
Footnotes
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Contributors BG, EH and UK contributed to writing and editing the manuscript. BG obtained consent from the patient. MMC was directly involved in patient care, and supervising and editing the manuscript.
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Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
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Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.
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Competing interests None declared.
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Provenance and peer review Not commissioned; externally peer reviewed.
- © BMJ Publishing Group Limited 2022. No commercial re-use. See rights and permissions. Published by BMJ.
References
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