Citation
Shalhout SZ, Emerick KS, Kaufman HL, Miller DM. Clinical utility of cell-free DNA liquid biopsies in Merkel cell carcinoma. Dermatology Online Journal. 2021.
Why this study matters
Merkel cell carcinoma lacks a universally reliable blood-based biomarker. Viral oncoprotein antibody titers are clinically useful in many patients, but they are not informative for all virus-negative tumors and may be less reliable in some immunosuppressed or immunotherapy-treated patients.
This study examined whether commercially available plasma cell-free DNA sequencing could provide a complementary, noninvasive method for detecting active disease and supporting clinical decision-making across both virus-positive and virus-negative MCC.
Cell-free DNA was closely associated with active MCC and tracked tumor burden particularly well in virus-negative disease. The study did not establish a validated surveillance assay, but it provided early evidence that liquid biopsy could become clinically useful when conventional biomarkers, imaging, or tissue biopsy are limited.
The cohort at a glance
Patients with MCC
All underwent plasma cfDNA sequencing using the commercially available Guardant360 platform.
Most patients had advanced disease
Disease status was assessed at the time of blood collection using clinical and radiographic evaluation.
Matched tumor and plasma variants
Every virus-negative patient with regional or distant disease had at least one concordant alteration.
What the study found
- cfDNA detection was strongly associated with active MCC at the time of blood collection.
- Virus-negative patients with regional or distant disease consistently had plasma alterations matching the primary tumor.
- No cfDNA was detected in patients with no evidence of disease or only a localized sub-centimeter lesion.
- In virus-negative disease, the highest plasma variant allele fraction correlated with measured tumor burden.
- Virus-positive tumors produced less specific genomic signals, consistent with their lower mutation burden.
Where liquid biopsy may help
Confirming difficult-to-biopsy disease
Plasma alterations concordant with the primary tumor may support metastatic disease when tissue acquisition is risky or technically challenging.
Detecting occult progression
High-level cfDNA may reveal biologically active disease before progression becomes unequivocal on imaging.
Monitoring virus-negative MCC
cfDNA may fill an important biomarker gap for patients in whom viral oncoprotein antibody surveillance is unavailable.
Supporting serial surveillance
Repeated blood sampling could eventually offer a less invasive way to follow molecular disease burden over time.
A clinically instructive case
One patient developed an atrial mass that could not be readily distinguished from thrombus on imaging. Liquid biopsy identified plasma mutations concordant with the primary MCC and returned before a technically difficult cardiac biopsy confirmed metastatic disease.
The result supported earlier treatment planning and illustrated the potential value of a high-fidelity blood-based biomarker when tissue confirmation is delayed, invasive, or hazardous.
Liquid biopsy should not replace tissue diagnosis or imaging. Its most plausible near-term role is complementary: helping resolve ambiguous disease status, strengthening confidence in metastatic attribution, and identifying patients whose molecular disease burden appears out of proportion to current imaging.
Important limitations
- The analysis included only 16 patients from a single institution.
- Testing was performed at physician discretion rather than through a fixed prospective sampling schedule.
- Low-frequency alterations in virus-positive patients could reflect clonal hematopoiesis rather than tumor-derived DNA.
- The commercial panel was not designed specifically for MCC or individualized to each patient's tumor.
- Larger longitudinal studies with serial blood collection are needed before routine surveillance use can be established.
What came next
The findings anticipated a broader shift toward tumor-informed and highly sensitive circulating tumor DNA assays in cutaneous oncology. Personalized panels built from each patient's tumor may be especially important for virus-positive MCC, where low mutation burden can limit the sensitivity of broad commercial sequencing platforms.
Authors
Sophia Z. Shalhout, Kevin S. Emerick, Howard L. Kaufman, and David M. Miller.