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PURPOSE: Merkel cell carcinoma (MCC) is an aggressive skin cancer with a 40% recurrence rate, lacking effective prognostic biomarkers and surveillance methods. This prospective, multicenter, observational study aimed to evaluate circulating tumor DNA (ctDNA) as a biomarker for detecting MCC recurrence. METHODS: Plasma samples, clinical data, and imaging results were collected from 319 patients. A tumor-informed ctDNA assay was used for analysis. Patients were divided into discovery (167 patients) and validation (152 patients) cohorts. Diagnostic performance, including sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), was assessed. RESULTS: ctDNA showed high sensitivity, 95% (discovery; 95% CI, 87 to 99) and 94% (validation; 95% CI, 85 to 98), for detecting disease at enrollment, with corresponding specificities of 90% (95% CI, 82 to 95) and 86% (95% CI, 77 to 93). A positive ctDNA during surveillance indicated increased recurrence risk, with hazard ratios (HRs) of 6.8 (discovery; 95% CI, 2.9 to 16) and 20 (validation; 95% CI, 8.3 to 50). The PPV for clinical recurrence at 1 year after a positive ctDNA test was 69% (discovery; 95% CI, 32 to 91) and 94% (validation; 95% CI, 71 to 100), respectively. The NPV at 135 days after a negative ctDNA test was 94% (discovery; 95% CI, 90 to 97) and 93% (validation; 95% CI, 89 to 97), respectively. Patients positive for ctDNA within 4 months after treatment had higher rates of recurrence, with 1-year rates of 74% versus 21% (adjusted HR, 7.4 [95% CI, 2.7 to 20]). CONCLUSION: ctDNA testing exhibited high prognostic accuracy in detecting MCC recurrence, suggesting its potential to reduce frequent surveillance imaging. ctDNA also identifies high-risk patients who need more frequent imaging and may be best suited for adjuvant therapy trials.
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BACKGROUND: Optimal duration of treatment (DoT) with immune checkpoint inhibitors (ICI) in metastatic cancers remains unclear. Many patients, especially those without radiologic complete remission, develop progressive disease after ICI discontinuation. Extending DoT with ICI may potentially improve efficacy outcomes but presents major logistical and cost challenges with standard frequency dosing (SFD). Receptor occupancy data supports reduced frequency dosing (RFD) of anti-PD-1 antibodies, which may represent a more practical and economically viable option to extend DoT. METHODS: We conducted a retrospective study of patients with metastatic melanoma and Merkel cell carcinoma (MCC), who received ICI at RFD administered every 3 months, after initial disease control at SFD. We evaluated efficacy, safety, and cost-savings of the RFD approach in this cohort. RESULTS: Between 2014 and 2021, 23 patients with advanced melanoma (N = 18) or MCC (N = 5) received anti-PD-1 therapy at RFD. Median DoT was 1.1 years at SFD and 1.2 years at RFD. The 3 year PFS after start of RFD was 73% in melanoma and 100% in MCC patients, which compare favorably to historical control rates. In the subset of 15 patients who received at least 2 years of therapy, total savings amounted to $1.1 million in drug costs and 384 h saved despite the extended DoT (median 3.4 years), as compared to the calculated cost of 2 years at SFD. CONCLUSIONS: ICI administration at RFD can allow extension of treatment duration, while preserving efficacy and reducing logistical and financial burden. RFD approach deserves further exploration in prospective clinical trials.