Circulating Tumor DNA Predicts Outcome from First-, but not Second-line Treatment and Identifies Melanoma Patients Who May Benefit from Combination Immunotherapy

Immunotherapy in melanoma: advances, pitfalls, and future perspectives

Cutaneous melanoma is the deadliest and most aggressive form of skin cancer owing to its high capacity for metastasis. Over the past few decades, the management of this type of malignancy has undergone a significant revolution with the advent of both targeted therapies and immunotherapy, which have greatly improved patient quality of life and survival. Nevertheless, the response rates are still unsatisfactory for the presence of side effects and development of resistance mechanisms. In this context, tumor microenvironment has emerged as a factor affecting the responsiveness and efficacy of immunotherapy, and the study of its interplay with the immune system has offered new promising clinical strategies. This review provides a brief overview of the currently available immunotherapeutic strategies for melanoma treatment by analyzing both the positive aspects and those that require further improvement. Indeed, a better understanding of the mechanisms involved in the immune evasion of melanoma cells, with particular attention on the role of the tumor microenvironment, could provide the basis for improving current therapies and identifying new predictive biomarkers.

US physician perspective on the use of biomarker and ctDNA testing in patients with melanoma

New treatments have increased survival of patients with melanoma, and methods to monitor patients throughout the disease process are needed. Circulating tumor DNA (ctDNA) is a predictive and prognostic biomarker that may allow routine, real-time monitoring of disease status. We surveyed 44 US physicians to understand their preferences and practice patterns for biomarker and ctDNA testing in their patients with melanoma. Tumor biomarker testing was often ordered in stage IIIA-IV patients. Barriers to biomarker testing include insufficient tissue (60%) and lack of insurance coverage (54%). ctDNA testing was ordered by 16-18% of physicians for stages II-IV. Reasons for not using ctDNA testing included lack of prospective data (41%), ctDNA testing used for research only (18%), and others. Physicians (≥74%) believed that ctDNA assays could help with monitoring and treatment selection throughout the disease process. Physicians consider ctDNA testing potentially valuable for clinical decision-making but cited concerns that should be addressed.

A multiparameter liquid biopsy approach allows to track melanoma dynamics and identify early treatment resistance

Melanoma heterogeneity is a hurdle in metastatic disease management. Although the advent of targeted therapy has significantly improved patient outcomes, the occurrence of resistance makes monitoring of the tumor genetic landscape mandatory. Liquid biopsy could represent an important biomarker for the real-time tracing of disease evolution. Thus, we aimed to correlate liquid biopsy dynamics with treatment response and progression by devising a multiplatform approach applied to longitudinal melanoma patient monitoring. We conceived an approach that exploits Next Generation Sequencing (NGS) and droplet digital PCR, as well as the FDA-cleared platform CellSearch, to analyze circulating tumor DNA (ctDNA) trend and circulating melanoma cell (CMC) count, together with their customized genetic and copy number variation analysis. The approach was applied to 17 stage IV melanoma patients treated with BRAF/MEK inhibitors, followed for up to 28 months. BRAF mutations were detected in the plasma of 82% of patients. Single nucleotide variants known or suspected to confer resistance were identified in 70% of patients. Moreover, the amount of ctDNA, both at baseline and during response, correlated with the type and duration of the response itself, and the CMC count was confirmed to be a prognostic biomarker. This work provides proof of principle of the power of this approach and paves the way for a validation study aimed at evaluating early ctDNA-guided treatment decisions in stage IV melanoma. The NGS-based molecular profile complemented the analysis of ctDNA trend and, together with CMC analysis, revealed to be useful in capturing tumor evolution.

Predictive Factors in Metastatic Melanoma Treated with Immune Checkpoint Inhibitors: From Clinical Practice to Future Perspective

The introduction of immunotherapy revolutionized the treatment landscape in metastatic melanoma. Despite the impressive results associated with immune checkpoint inhibitors (ICIs), only a portion of patients obtain a response to this treatment. In this scenario, the research of predictive factors is fundamental to identify patients who may have a response and to exclude patients with a low possibility to respond. These factors can be host-associated, immune system activation-related, and tumor-related. Patient-related factors can vary from data obtained by medical history (performance status, age, sex, body mass index, concomitant medications, and comorbidities) to analysis of the gut microbiome from fecal samples. Tumor-related factors can reflect tumor burden (metastatic sites, lactate dehydrogenase, C-reactive protein, and circulating tumor DNA) or can derive from the analysis of tumor samples (driver mutations, tumor-infiltrating lymphocytes, and myeloid cells). Biomarkers evaluating the immune system activation, such as IFN-gamma gene expression profile and analysis of circulating immune cell subsets, have emerged in recent years as significantly correlated with response to ICIs. In this manuscript, we critically reviewed the most updated literature data on the landscape of predictive factors in metastatic melanoma treated with ICIs. We focus on the principal limits and potentiality of different methods, shedding light on the more promising biomarkers.

Promising and Minimally Invasive Biomarkers: Targeting Melanoma

The therapeutic landscape of malignant melanoma has been radically reformed in recent years, with novel treatments emerging in both the field of cancer immunotherapy and signalling pathway inhibition. Large-scale tumour genomic characterization has accurately classified malignant melanoma into four different genomic subtypes so far. Despite this, only somatic mutations in BRAF oncogene, as assessed in tumour biopsies, has so far become a validated predictive biomarker of treatment with small molecule inhibitors. The biology of tumour evolution and heterogeneity has uncovered the current limitations associated with decoding genomic drivers based only on a single-site tumour biopsy. There is an urgent need to develop minimally invasive biomarkers that accurately reflect the real-time evolution of melanoma and that allow for streamlined collection, analysis, and interpretation. These will enable us to face challenges with tumour tissue attainment and process and will fulfil the vision of utilizing "liquid biopsy" to guide clinical decisions, in a manner akin to how it is used in the management of haematological malignancies. In this review, we will summarize the most recent published evidence on the role of minimally invasive biomarkers in melanoma, commenting on their future potential to lead to practice-changing discoveries.

Detectable ctDNA at the time of treatment cessation of ipilimumab and nivolumab for toxicity predicts disease progression in advanced melanoma patients

Background

Immune checkpoint inhibition (ICI) has led to unprecedented outcomes for melanoma patients but is associated with toxicity. ICI resumption after high grade irAEs poses a significant challenge in the clinical management of melanoma patients and there are no biomarkers that can help identify patients that might benefit from resuming treatment. This study aims to determine if circulating tumor DNA (ctDNA) levels at the time of treatment-limiting irAE could guide treatment decisions in this clinical context.

Methods

This is a retrospective exploratory biomarker study from 34 patients treated with combination ICI for stage IV melanoma. Patients had a treatment-limiting toxicity and a baseline plasma collection prior to commencing ICI and within 6 weeks of stopping therapy. Blood samples were tested for ctDNA at baseline and cessation therapy.

Results

Median progression free survival (PFS) and overall survival (OS) have not been reached (24-month PFS rate 54% and OS rate 72.3%). PD occurred in 47% (16/34) of patients. Median PFS with detectable ctDNA from plasma collected at the time of toxicity was 6.5 months while not reached (NR) with undetectable levels (HR: 4.0, 95% CI 0.95-17.5, p=0.0023). Median OS with detectable ctDNA at cessation for toxicity was 19.4 months and NR for undetectable ctDNA (HR: 3.9, 95%CI 20.8-18.6, p=0.024). Positive ctDNA at the time of cessation was highly specific (specificity 0.94, 95% CI 0.74-0.99, PPV 0.88, 95% CI 0.53-0.99). However, ctDNA negativity has low sensitivity as a predictor of ongoing disease control (sensitivity 0.437, 95% CI 0.23-0.67). Notably, 4/9 (44%) ctDNA negative patients who had disease progression had brain only disease progression.

Conclusions

Undetectable ctDNA and CR on imaging after stopping immunotherapy for toxicity results in high rates of long-term durable control. For patients with immunotherapy related toxicity, who have persistent ctDNA at 8 - 12 weeks, the risk of disease progression is significant.

Tumour-agnostic plasma assay for circulating tumour DNA predicts outcome in recurrent and/or metastatic squamous cell carcinoma of the head and neck treated with a PD-1 inhibitor

BACKGROUND

Only 15-20% of recurrent and/or metastatic squamous cell carcinoma of the head and neck (R/M SCCHN) patients derive long-term benefit from nivolumab or pembrolizumab. We developed a circulating tumour DNA (ctDNA) tumour-agnostic assay aimed at the early prediction of single agent programmed cell death 1 (PD1) inhibitor efficacy in R/M SCCHN.

PATIENTS AND METHODS

Our tumour-agnostic assay included 37 genes frequently mutated in R/M SCCHN and two HPV16 genes. Primary endpoint was the concordance between ctDNA kinetics (ΔctDNA) and the best overall response according to Response Evaluation Criteria in Solid Tumors version 1.1. ΔctDNA was defined as the difference in mean variant allele frequency (VAF) between the on-treatment sample harvested 6-10 weeks (FU1) after PD1 inhibitor initiation and the pre-treatment plasma sample (ΔctDNA = mean FU1 VAF - mean pre-treatment VAF).

RESULTS

ctDNA was detected in 35/44 (80%) of the pre-treatment plasma samples. The concordance between ΔctDNA and imaging response was observed in 74%. Median progression-free survival was 8.6 months in the favourable ΔctDNA group and 2.5 months in the unfavourable ΔctDNA group (p = 0.057). Median overall survival (OS) was 18.1 and 8.2 months in the favourable and unfavourable ΔctDNA groups, respectively (p = 0.13). In patients with PD-L1 expressing SCCHN (Combined Positive Score ≥1), OS was significantly better in patients with favourable ΔctDNA compared with patients with unfavourable ΔctDNA: median OS was 41.5 and 8.4 months (p = 0.033), respectively.

CONCLUSIONS

Tumour-agnostic ctDNA analysis for human papillomavirus (HPV)-negative and HPV-positive R/M SCCHN is feasible. ctDNA kinetics show promising results in predicting the efficacy of PD1 inhibitors in R/M SCCHN.

The dynamics of circulating tumour DNA (ctDNA) during treatment reflects tumour response in advanced melanoma patients

Despite the introduction of targeted (BRAFi/MEKi) and immune checkpoint inhibitors (ICIs) has significantly reduced the recurrence rate and improved the overall survival (OS) of patients with Stage III and IV melanoma, only a percentage will benefit of durable disease control. The aim of this study was to examine whether the levels of circulating tumour DNA (ctDNA) in plasma of advanced melanoma patients undergoing BRAFi/MEKi or ICIs vary according to the patients' survival outcomes (i.e. progression-free survival (PFS) and OS) and disease progression. Plasma samples of Stage III-IV melanoma patients were collected at baseline (treatment initiation) and thereafter every 3 months. Circulating BRAFV600E/K and NRASQ61R/K mutations were analysed through droplet digital PCR (ddPCR, Bio-Rad) in a total of 177 plasma samples from 48 melanoma patients (19 Stage III, 29 Stage IV). Baseline ctDNA concentration was significantly associated with OS (HR = 1.003, 95% CI = 1.000-1.006, p = 0.043) and PFS (HR = 1.004, 95% CI = 1.000-1.007, p = 0.029) independent of clinical-prognostic confounders. For each unit increase in the ∆ctDNA (concentration difference between the last follow-up and baseline) there was a 24% increased risk of disease progression, irrespective of treatment type and stage at diagnosis (OR = 1.24, 95% CI = 1.03-1.49, p = 0.020, AUC = 0.93). Patients with reduction of ctDNA level from baseline to the last follow-up had longer OS (HR = 0.14; 95% CI = 0.05-0.44, p = 0.001) and PFS (HR = 0.08; 95% CI = 0.03-0.27, p < 0.0001) compared to patients with increased ctDNA, including adjustment for confounding factors. Our findings suggest that variation of ctDNA over time during melanoma treatment reflects the clinical outcome and tumour response to therapy and might be helpful in clinical monitoring.

Cured or Not? Long-term Outcomes of Immunotherapy Responders. Focus on Melanoma

PURPOSE OF REVIEW

Immune checkpoint inhibitors (ICIs) demonstrated robust antitumor activity and tolerable safety in advanced melanoma. Data on long-term outcome of patients who benefited from this therapy and who are still free of progression despite ICI discontinuation is now available. We review here the characteristics of long-term ICI responders and address the critical question of cure.

RECENT FINDINGS

Long-term outcome of patients with metastatic melanoma enrolled in large phase 2 and phase 3 clinical trials evaluating ICI in metastatic melanoma is now available. Durable responses, with more than 6 years of median follow-up, may persist after discontinuation. They occur more frequently in patients who achieved a complete response rather than in patients who had partial response or stable disease. Although long-term clinical benefit is more frequent in patients with high PDL-1 expression and smaller tumor burden, durable response may also be observed regardless of baseline characteristics. In patients with asymptomatic brain metastasis, combined immunotherapy (ipilimumab plus nivolumab) may also lead to long-term remission. Clinical trials confirm the durable antitumor activity of ICI. Although the hope for cure seems reasonable for many patients in this situation, late relapses may occur and no relapse-predictive biomarkers have been identified yet. Long-term responders who relapse can respond to a rechallenge of ICI although data are limited concerning the rate and the duration of this new response.

Circulating Cell-Free DNA as a Biomarker for Prognosis and Response to Systemic Therapy in Patients with Unresectable Hepatocellular Carcinoma

INTRODUCTION

Systemic therapy provides clinical benefits to a subset of patients with advanced unresectable hepatocellular carcinoma (HCC). However, few biomarkers are available for predicting prognosis and treatment response in patients with advanced HCC undergoing treatment with systemic therapies. This study aimed to examine whether circulating cell-free DNA (cfDNA) containing circulating tumor DNA can act as a therapeutic response and prognostic biomarker in patients with advanced HCC.

METHODS

We analyzed longitudinally collected plasma cfDNA of patients with advanced HCC who were naïve to systemic therapy, and assessed their prognostic and predictive values to determine treatment responses.

RESULTS

cfDNA concentration positively correlated with entire tumor volume on computed tomography before (p = 0.0231) and at the end (p < 0.0001) of the first-line systemic therapy. The overall survival rate was higher in patients with cfDNA concentrations lower than the median cfDNA level at baseline compared to patients with higher cfDNA concentrations (hazard ratio, 0.2765; 95% confidence interval, 0.08-0.81; p = 0.0197). The ratio of cfDNA at 4 weeks to that at baseline was predictive of radiographic disease response. In patients with progressive disease, cfDNA concentration at 4 weeks increased significantly (p = 0.0245), whereas the concentration remained unchanged in patients with other disease courses (p = 0.9375).

CONCLUSION

The baseline plasma cfDNA concentration can be used as a prognostic biomarker in patients with advanced HCC. cfDNA kinetics may also predict the tumor response to therapy and disease progression.

Feasibility of personalized circulating tumor DNA detection in stage II and III melanoma

The objective of this study was to evaluate the feasibility of developing personalized, tumor-informed assays for patients with high-risk resectable melanoma and examine circulating tumor DNA (ctDNA) levels in relation to clinical status. Pilot prospective study of clinical stage IIB/C and resectable stage III melanoma patients. Tumor tissue was used to design bespoke somatic assays for interrogating ctDNA in patients' plasma using a multiplex PCR (mPCR) next-generation sequencing (NGS)-based approach. Plasma samples for ctDNA analysis were collected pre-/post-surgery and during surveillance. Out of 28 patients (mean 65 years, 50% male), 13 (46%) had detectable ctDNA prior to definitive surgery and 96% (27/28) tested ctDNA-negative within 4 weeks post-surgery. Pre-surgical detection of ctDNA was significantly associated with the later-stage (P = 0.02) and clinically evident stage III disease (P = 0.007). Twenty patients continue in surveillance with serial ctDNA testing every 3-6 months. With a median follow-up of 443 days, six out of 20 (30%) patients developed detectable ctDNA levels during surveillance. All six of these patients recurred with a mean time to recurrence of 280 days. Detection of ctDNA in surveillance preceded the diagnosis of clinical recurrence in three patients, was detected concurrent with clinical recurrence in two patients and followed clinical recurrence in one patient. One additional patient developed brain metastases without detection of ctDNA during surveillance but had positive pre-surgical ctDNA. Our results demonstrate the feasibility of obtaining a personalized, tumor-informed mPCR NGS-based ctDNA assay for patients with melanoma, particularly in resectable stage III disease.

Circulating Tumor DNA: The Dawn of a New Era in the Optimization of Chemotherapeutic Strategies for Metastatic Colo-Rectal Cancer Focusing on RAS Mutation

Genotyping of tumor tissues to assess RAS and BRAF V600E mutations enables us to select optimal molecularly targeted therapies when considering treatment strategies for patients with metastatic colorectal cancer. Tissue-based genetic testing is limited by the difficulty of performing repeated tests, due to the invasive nature of tissue biopsy, and by tumor heterogeneity, which can limit the usefulness of the information it yields. Liquid biopsy, represented by circulating tumor DNA (ctDNA), has attracted attention as a novel method for detecting genetic alterations. Liquid biopsies are more convenient and much less invasive than tissue biopsies and are useful for obtaining comprehensive genomic information on primary and metastatic tumors. Assessing ctDNA can help track genomic evolution and the status of alterations in genes such as RAS, which are sometimes altered following chemotherapy. In this review, we discuss the potential clinical applications of ctDNA, summarize clinical trials focusing on RAS, and present the future prospects of ctDNA analysis that could change daily clinical practice.

Metastatic Melanoma: Liquid Biopsy as a New Precision Medicine Approach

Precision medicine has driven a major change in the treatment of many forms of cancer. The discovery that each patient is different and each tumor mass has its own characteristics has shifted the focus of basic and clinical research to the singular individual. Liquid biopsy (LB), in this sense, presents new scenarios in personalized medicine through the study of molecules, factors, and tumor biomarkers in blood such as circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), exosomes and circulating tumor microRNAs (ct-miRNAs). Moreover, its easy application and complete absence of contraindications for the patient make this method applicable in a great many fields. Melanoma, given its highly heterogeneous characteristics, is a cancer form that could significantly benefit from the information linked to liquid biopsy, especially in the treatment management. In this review, we will focus our attention on the latest applications of liquid biopsy in metastatic melanoma and possible developments in the clinical setting.

Changes in circulating tumor DNA and outcomes in solid tumors treated with immune checkpoint inhibitors: a systematic review

BACKGROUND

Quantification of circulating tumor DNA (ctDNA) levels is a reliable prognostic tool in several malignancies. Dynamic changes in ctDNA levels in response to treatment may also provide prognostic information. Here, we explore the value of changes in ctDNA levels in response to immune checkpoint inhibitors (ICIs).

METHODS

We searched MEDLINE (host: PubMed) for trials of ICIs in advanced solid tumors in which outcomes were reported based on change in ctDNA levels. ctDNA reduction was defined as reported in individual trials. Typically, this was either >50% reduction or a reduction to undetectable levels. We extracted HRs and related 95% CIs and/or p values comparing ctDNA reduction versus no reduction for progression-free survival (PFS) and/or overall survival (OS). Data were then pooled in a meta-analysis. Variation in effect size was examined using subgroup analyses.

RESULTS

Eighteen trials were included in the meta-analysis. ctDNA levels were detectable in all participants in all studies prior to initiation of ICIs. A reduction in ctDNA measured 6-16 weeks after starting treatment was associated with significantly better PFS (HR 0.20; 95% CI, 0.14 to 0.28; p<0.001). Similarly, OS was superior in patients with reduced ctDNA levels (HR 0.18; 95% CI, 0.12 to 0.26; p<0.001). The results were consistent across all disease sites, lines of treatment, magnitude of change (to undetectable vs >50% reduction) and whether treatment exposure comprised single or combination ICIs.

CONCLUSIONS

In advanced solid tumors, a reduction in ctDNA levels in response to ICIs is associated with substantial improvements in outcome. ctDNA change is an early response biomarker which may allow for de-escalation of cross-sectional imaging in patients receiving ICIs or support treatment de-escalation strategies.

Shaping the Future of Immunotherapy Targets and Biomarkers in Melanoma and Non-Melanoma Cutaneous Cancers

Recent advances in treating cutaneous melanoma have resulted in impressive patient survival gains. Refinement of disease staging and accurate patient risk classification have significantly improved our prognostic knowledge and ability to accurately stratify treatment. Undoubtedly, the most important step towards optimizing patient outcomes has been the advent of cancer immunotherapy, in the form of immune checkpoint inhibition (ICI). Immunotherapy has established its cardinal role in the management of both early and late-stage melanoma. Through leveraging outcomes in melanoma, immunotherapy has also extended its benefit to other types of skin cancers. In this review, we endeavor to summarize the current role of immunotherapy in melanoma and non-melanoma skin cancers, highlight the most pertinent immunotherapy-related molecular biomarkers, and lastly, shed light on future research directions.

Gut microbiota diversity and composition in predicting immunotherapy response and immunotherapy-related colitis in melanoma patients: A systematic review

BACKGROUND

Gut microbiome (GM) composition and diversity have recently been studied as a biomarker of response to immune checkpoint blockade therapy (ICB) and of ICB-related colitis.

AIM

To conduct a systematic review on the role of GM composition and diversity in predicting response and colitis in patients with melanoma treated with ICB.

METHODS

The review protocol was registered in PROSPERO: CRD42021228018. From a total of 300 studies, nine studies met inclusion criteria. Two studies were phase I clinical trials, while the remainder were prospective observational studies. All but one study has moderate risk of bias. In addition, we conducted a relevant search by Reference Citation Analysis (RCA) (https://www.referencecitationanalysis.com).

RESULTS

Fecal samples enriched in Firmicutes phylum were associated with good response to ICB, whereas the Bacteroidales family was associated with poor response to ICB. Samples with greater GM diversity were associated with more favorable response to ICB [hazard ratio (HR) = 3.57, 95% confidence interval = 1.02-12.52, P < 0.05]. Fecal samples with a higher abundance in Firmicutes were more susceptible to ICB-related colitis (P < 0.01) whereas samples enriched in Bacteroidetes were more resistant to ICB-related colitis (P < 0.05). Overall, there was limited concordance in the organisms in the GM identified to be associated with response to ICB, and studies evaluating GM diversity showed conflicting results.

CONCLUSION

This highlights the need for further prospective studies to confirm whether the GM could be used as a biomarker and potential intervention to modulate ICB response in melanoma patients.

The amount of DNA combined with TP53 mutations in liquid biopsy is associated with clinical outcome of renal cancer patients treated with immunotherapy and VEGFR-TKIs

BACKGROUND

Despite the increasing number of treatment options, reliable prognostic/predictive biomarkers are still missing for patients affected by metastatic clear cell renal cell carcinoma (mccRCC).

METHODS

Patients with mccRCC undergoing standard first line treatment were enrolled. Blood (12 ml) was drawn at treatment baseline and circulating free DNA (cfDNA) was extracted from plasma. Next-generation sequencing (NGS) was performed on cfDNA using the Oncomine Pan-Cancer Cell-Free Assay and clinical outcomes were correlated with liquid biopsy findings.

RESULTS

A total of 48 patients were enrolled, 12 received immunotherapy and 36 received a vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor (TKI). A cfDNA cut-off of 0.883 ng/μl stratified patients based on progression-free survival (PFS) and overall survival (OS) (p = 0.001 and p = 0.008, respectively). cfDNA amount was also correlated with best response (p = 0.006). Additional cfDNA cut-points divided patients into short, intermediate and long responders, with PFS of 4.87 vs 9.13 vs 23.1 months, respectively (p < 0.001). PFS resulted to be significantly shorter in carriers of mutant TP53 compared to not carriers (p = 0.04). Patients with high cfDNA levels and mutant TP53 have the worst PFS, while patients with low cfDNA amounts and no mutations in TP53 displayed the longest PFS (p = 0.004).

CONCLUSIONS

The present study demonstrates that cfDNA and TP53 are potential predictive biomarkers of response in mccRCC to be further explored in larger and/or prospective studies.

Skin Cancer Research Goes Digital: Looking for Biomarkers within the Droplets

Skin cancer, which includes the most frequent malignant non-melanoma carcinomas (basal cell carcinoma, BCC, and squamous cell carcinoma, SCC), along with the difficult to treat cutaneous melanoma (CM), pose important worldwide issues for the health care system. Despite the improved anti-cancer armamentarium and the latest scientific achievements, many skin cancer patients fail to respond to therapies, due to the remarkable heterogeneity of cutaneous tumors, calling for even more sophisticated biomarker discovery and patient monitoring approaches. Droplet digital polymerase chain reaction (ddPCR), a robust method for detecting and quantifying low-abundance nucleic acids, has recently emerged as a powerful technology for skin cancer analysis in tissue and liquid biopsies (LBs). The ddPCR method, being capable of analyzing various biological samples, has proved to be efficient in studying variations in gene sequences, including copy number variations (CNVs) and point mutations, DNA methylation, circulatory miRNome, and transcriptome dynamics. Moreover, ddPCR can be designed as a dynamic platform for individualized cancer detection and monitoring therapy efficacy. Here, we present the latest scientific studies applying ddPCR in dermato-oncology, highlighting the potential of this technology for skin cancer biomarker discovery and validation in the context of personalized medicine. The benefits and challenges associated with ddPCR implementation in the clinical setting, mainly when analyzing LBs, are also discussed.

The oligometastatic spectrum in the era of improved detection and modern systemic therapy

Metastases remain the leading cause of cancer-related mortality. The oligometastasis hypothesis postulates that a spectrum of metastatic spread exists and that some patients with a limited burden of metastases can be cured with ablative therapy. Over the past decade, substantial advances in systemic therapies have resulted in considerable improvements in the outcomes of patients with metastatic cancers, warranting re-examination of the oligometastatic paradigm and the role of local ablative therapies within the context of the improved therapeutic responses, shifting patterns of disease recurrence and possible synergy with systemic treatments. Herein, we reframe the oligometastatic phenotype as a dynamic state for which locally ablative, metastasis-directed therapy improves clinical outcomes, including by prolonging survival and increasing cure rates. Important risk factors defining the metastatic spectrum are highlighted that inform both staging and therapy. Finally, we synthesize the literature on combining local therapies with modern systemic treatments, identifying general themes to optimally integrate ablative therapies in this context.

Charting roadmaps towards novel and safe synergistic immunotherapy combinations

Checkpoint inhibitor-based cancer immunotherapy is often combined in the clinic with other immunotherapy strategies, targeted therapies, chemotherapy or standard-of-care treatments to achieve superior therapeutic efficacy. The large number of immunotherapy combinations that are currently undergoing clinical testing necessitate the establishment of faithful criteria to prioritize optimal combinations with evidence of synergy, to determine their safety and optimal sequence of administration and to identify biomarkers of therapy resistance and response. In this review, we focus on recent developments in immunotherapy combinations and reflect on how combinations should be optimized to maximize the impact of immunotherapy in clinical oncology.

Anchored Multiplex PCR Custom Melanoma Next Generation Sequencing Panel for Analysis of Circulating Tumor DNA

Detection of melanoma mutations using circulating tumor DNA (ctDNA) is a potential alternative to using genomic DNA from invasive tissue biopsies. To date, mutations in the GC-rich TERT promoter region, which is commonly mutated in melanoma, have been technically difficult to detect in ctDNA using next-generation sequencing (NGS) panels. In this study, we developed a custom melanoma NGS panel for detection of ctDNA, which encompasses the top 15 gene mutations in melanoma including the TERT promoter. We analyzed 21 stage III and IV melanoma patient samples who were treatment-naïve or on therapy. The overall detection rate of the custom panel, based on BRAF/NRAS/TERT promoter mutations, was 14/21 (67%) patient samples which included a TERT C250T mutation in one BRAF and NRAS mutation negative sample. A BRAF or NRAS mutation was detected in the ctDNA of 13/21 (62%) patients while TERT promoter mutations were detected in 10/21 (48%) patients. Co-occurrence of TERT promoter mutations with BRAF or NRAS mutations was found in 9/10 (90%) patients. The custom ctDNA panel showed a concordance of 16/21 (76%) with tissue based-detection and included 12 BRAF/NRAS mutation positive and 4 BRAF/NRAS mutation negative patients. The ctDNA mutation detection rate for stage IV was 12/16 (75%) and for stage III was 1/5 (20%). Based on BRAF, NRAS and TERT promoter mutations, the custom melanoma panel displayed a limit of detection of ~0.2% mutant allele frequency and showed significant correlation with droplet digital PCR. For one patient, a novel MAP2K1 H119Y mutation was detected in an NRAS/BRAF/TERT promoter mutation negative background. To increase the detection rate to >90% for stage IV melanoma patients, we plan to expand our custom panel to 50 genes. This study represents one of the first to successfully detect TERT promoter mutations in ctDNA from cutaneous melanoma patients using a targeted NGS panel.

Current Trends in Circulating Biomarkers for Melanoma Detection

Melanomas have increased in global incidence and are the leading cause of skin cancer deaths. Whilst the majority of early-stage, non-metastatic melanomas can be cured with surgical excision alone, ~5% of patients with early melanomas will experience recurrence following a variable disease-free interval and progression to metastatic melanoma and ultimately death. This is likely because of primary tumor heterogeneity and progressive clonal divergency resulting in the growth of more aggressive tumor populations. Liquid biomarkers have the advantage of real-time, non-invasive longitudinal monitoring of tumor burden and heterogeneity over tissue markers. Currently, the only serological marker used in the staging and monitoring of melanoma is serum lactate dehydrogenase, which is not sufficiently specific or sensitive, and is not used routinely in all centers. An ideal melanoma biomarker would be used to identify patients who are at high-risk of primary melanoma, screen for relapse, detect early-stage melanoma, provide treatment outcomes to personalize systemic treatment, follow tumor heterogeneity, provide prognostic data before, during and after treatment, and monitor response to treatment. This review provides a summary of the current research in this field with a specific focus on circulating tumor cells, circulating tumor DNA, microRNA, and extracellular vesicles which may serve to suit these goals.

Circulating Tumour DNA in Melanoma-Clinic Ready?

PURPOSE OF REVIEW

Liquid biopsies, including circulating tumour DNA (ctDNA), can inform a variety of clinical questions. This review examines the potential role of ctDNA as a clinical tool to inform clinical decision-making from early to late stage cutaneous melanoma.

RECENT FINDINGS

In pre-clinical studies, ctDNA has been shown to detect minimal residual disease and molecular relapse; predict and monitor response to therapy; and identify key resistance mechanisms. Here, we examine the potential utility of ctDNA and discuss its limitations for use in patients with melanoma. We present novel clinical trials, which are testing its value as a tool to augment clinical decision-making. Finally, we discuss the steps that are needed to ensure that ctDNA is used optimally in order to improve outcomes for patients with melanoma. Preclinical studies have shown that ctDNA has huge potential to provide real-time information about disease status in patients with melanoma. It is now time to test it rigorously within clinical trials to assess how it can be optimally used to benefit patients in the clinic.

In an era of ctDNA, is metabolomics the new kid on the block?

Mass action drives the serum homeostasis of metabolites. Recent developments in biofluid metabolomics suggest the potential to harness these changes using small volumes of blood to diagnosis, monitor, and risk stratify cancer patients. This current study may represent a complementary technology to circulating tumor DNA detection.

Detection of clinical progression through plasma ctDNA in metastatic melanoma patients: a comparison to radiological progression

BACKGROUND

The validity of circulating tumour DNA (ctDNA) as an indicator of disease progression compared to medical imaging in patients with metastatic melanoma requires detailed evaluation.

METHODS

Here, we carried out a retrospective ctDNA analysis of 108 plasma samples collected at the time of disease progression. We also analysed a validation cohort of 66 metastatic melanoma patients monitored prospectively after response to systemic therapy.

RESULTS

ctDNA was detected in 62% of patients at the time of disease progression. For 67 patients that responded to treatment, the mean ctDNA level at progressive disease was significantly higher than at the time of response (P < 0.0001). However, only 30 of these 67 (45%) patients had a statistically significant increase in ctDNA by Poisson test. A validation cohort of 66 metastatic melanoma patients monitored prospectively indicated a 56% detection rate of ctDNA at progression, with only two cases showing increased ctDNA prior to radiological progression. Finally, a correlation between ctDNA levels and metabolic tumour burden was only observed in treatment naïve patients but not at the time of progression in a subgroup of patients failing BRAF inhibition (N = 15).

CONCLUSIONS

These results highlight the low efficacy of ctDNA to detect disease progression in melanoma when compared mainly to standard positron emission tomography imaging.

Current and Future Clinical Applications of ctDNA in Immuno-Oncology

Testing peripheral blood for circulating tumor DNA (ctDNA) offers a minimally invasive opportunity to diagnose, characterize, and monitor the disease in individual cancer patients. ctDNA can reflect the actual tumor burden and specific genomic state of disease and thus might serve as a prognostic and predictive biomarker for immune checkpoint inhibitor (ICI) therapy. Recent studies in various cancer entities (e.g., melanoma, non-small cell lung cancer, colon cancer, and urothelial cancer) have shown that sequential ctDNA analyses allow for the identification of responders to ICI therapy, with a significant lead time to imaging. ctDNA assessment may also help distinguish pseudoprogression under ICI therapy from real progression. Developing dynamic changes in ctDNA concentrations as a potential surrogate endpoint of clinical efficacy in patients undergoing adjuvant immunotherapy is ongoing. Besides overall ctDNA burden, further ctDNA characterization can help uncover tumor-specific determinants (e.g., tumor mutational burden and microsatellite instability) of responses or resistance to immunotherapy. In future studies, standardized ctDNA assessments need to be included in interventional clinical trials across cancer entities to demonstrate the clinical utility of ctDNA as a biomarker for personalized cancer immunotherapy.

Predictive molecular markers for the treatment with immune checkpoint inhibitors in colorectal cancer

Colorectal cancer is one of the most common malignant tumors and, hence, has become one of the most important public health issues in the world. Treatment with immune checkpoint inhibitors (ICIs) successfully improves the survival rate of patients with melanoma, non-small-cell lung cancer, and other malignancies, and its application in metastatic colorectal cancer is being actively explored. However, a few patients develop drug resistance. Predictive molecular markers are important tools to precisely screen patient groups that can benefit from treatment with ICIs. The current article focused on certain important predictive molecular markers for ICI treatment in colorectal cancer, including not only some of the mature molecular markers, such as deficient mismatch repair (d-MMR), microsatellite instability-high (MSI-H), tumor mutational burden (TMB), programmed death-ligand-1 (PD-L1), tumor immune microenvironment (TiME), and tumor-infiltrating lymphocytes (TILs), but also some of the novel molecular markers, such as DNA polymerase epsilon (POLE), polymerase delta 1 (POLD1), circulating tumor DNA (ctDNA), and consensus molecular subtypes (CMS). We have reviewed these markers in-depth and presented the results from certain important studies, which suggest their applicability in CRC and indicate their advantages and disadvantages. We hope this article is helpful for clinicians and researchers to systematically understand these markers and can guide the treatment of colorectal cancer.

Early identification of disease progression in ALK-rearranged lung cancer using circulating tumor DNA analysis

Targeted kinase inhibitors improve the prognosis of lung cancer patients with ALK alterations (ALK+). However, due to the emergence of acquired resistance and varied clinical trajectories, early detection of disease progression is warranted to guide patient management and therapy decisions. We utilized 343 longitudinal plasma DNA samples from 43 ALK+ NSCLC patients receiving ALK-directed therapies to determine molecular progression based on matched panel-based targeted next-generation sequencing (tNGS), and shallow whole-genome sequencing (sWGS). ALK-related alterations were detected in 22 out of 43 (51%) patients. Among 343 longitudinal plasma samples analyzed, 174 (51%) were ctDNA-positive. ALK variant and fusion kinetics generally reflected the disease course. Evidence for early molecular progression was observed in 19 patients (44%). Detection of ctDNA at therapy baseline indicated shorter times to progression compared to cases without mutations at baseline. In patients who succumbed to the disease, ctDNA levels were highly elevated towards the end of life. Our results demonstrate the potential utility of these NGS assays in the clinical management of ALK+ NSCLC.

Circulating tumour DNA (ctDNA) in metastatic melanoma, a systematic review and meta-analysis

INTRODUCTION

Circulating tumour DNA (ctDNA) is an emerging biomarker in melanoma. We performed a systematic review and meta-analysis to explore its clinical utility as a prognostic, pharmacodynamic (PD) and predictive biomarker.

METHODS

A systematic search was conducted from Jan 2015 to April 2021, of the electronic databases PubMed, Cochrane Library and Ovid MEDLINE to identify studies. Studies were restricted to those published in English within the last 5 years, evaluating ctDNA in humans in ≥10 patients. Survival data were extracted for meta-analysis using pooled treatment effect (TE), i.e. log hazard ratios (HRs) and corresponding standard error of TE for progression-free survival or overall survival differences in patients who were ctDNA positive or negative. PRISMA statement guidelines were followed.

RESULTS

A meta-analysis of 19 studies grouped according to methodology of ctDNA detection, revealed a combined estimate for HR of progression-free survival (13 studies using droplet digital Polymerase Chain Reaction (ddPCR) methodology (N = 1002) of 2.10 (95% CI: 1.71-2.59) revealing a poorer prognosis when ctDNA was detected. This result was confirmed in the smaller analysis of (non-ddPCR, N = 347) five studies: HR = 2.45 (95% CI: 1.29-4.63). Similar findings were found in the overall survival analysis of nine studies (ddPCR methodology, N = 841) where the combined HR was 2.78 (95% CI: 2.21-3.49) and of the five studies (non-ddPCR methodology, N = 326) where the combined HR was 2.58 (95% CI: 1.74-3.84). Serial ctDNA levels on treatment showed a pharmacodynamic role reflecting response or resistance earlier than radiological assessment.

CONCLUSIONS

Circulating tumour DNA is a predictive, prognostic and PD biomarker in melanoma. Technical standardisation of assays is required before clinical adoption.

The Prognostic Value of ctDNA and bTMB on Immune Checkpoint Inhibitors in Human Cancer

Background

Circulating tumor DNA (ctDNA) levels and blood tumor mutation burden (bTMB) have a significant impact on the prognosis of tumor patients. However, their prognostic role in immune checkpoint inhibitors (ICIs) in cancer patients is still unclear.

Methods

We used the Review Manager software (version 5.3) to perform a meta-analysis based on the published literature to explore the prognostic value of ctDNA and bTMB in patients receiving immunotherapy. We extracted the hazard ratios (HRs) of progression-free survival (PFS) and overall survival (OS) for each included study and their respective 95% confidence intervals (CIs) and p-values for analysis.

Results

Thirteen studies were included in the meta-analysis. Higher ctDNA levels were significantly associated with shorter OS (HR = 3.35, 95%CI = 2.49–4.51, p < 0.00001) and PFS (HR = 3.28, 95%CI = 2.47–4.35, p < 0.00001). The results of ctDNA subgroup analysis showed that high posttreatment ctDNA levels significantly correlated with shorter OS in cancer patients receiving ICIs (HR = 5.09, 95%CI = 1.43–18.07, p = 0.01). Moreover, patients with ctDNA clearance had better OS (HR = 4.94, 95%CI = 2.96–8.26, p < 0.00001). Patients with high posttreatment ctDNA levels had shorter PFS (HR = 3.00, 95%CI = 2.02–4.46, p < 0.00001) and those with ctDNA clearance had longer PFS (HR = 4.61, 95%CI = 2.78–7.65, p < 0.00001). However, there was no statistically significant difference in the OS benefits between a high and a low bTMB after ICI therapy (HR = 0.68, 95%CI = 0.33–1.37, p = 0.28).

Conclusions

The host immune system and tumor burden together determine whether cancer patients can benefit from ICI therapy. Our systematic review and meta-analysis revealed for the first time that the levels of pretreatment and posttreatment ctDNA and the clearance of ctDNA can independently be used as prognostic factors for antitumor immunotherapy, while bTMB cannot. In conclusion, ctDNA levels have great potential as an assistant tool for radiological assessments to make clinical therapeutic decisions. The prognostic utility of bTMB still requires further exploration.

Tumour burden and efficacy of immune-checkpoint inhibitors

Accumulating evidence suggests that a high tumour burden has a negative effect on anticancer immunity. The concept of tumour burden, simply defined as the total amount of cancer in the body, in contrast to molecular tumour burden, is often poorly understood by the wider medical community; nonetheless, a possible role exists in defining the optimal treatment strategy for many patients. Historically, tumour burden has been assessed using imaging. In particular, CT scans have been used to evaluate both the number and size of metastases as well as the number of organs involved. These methods are now often complemented by metabolic tumour burden, measured using the more recently developed 2-deoxy-2-[¹⁸F]-fluoro-D-glucose (FDG)-PET/CT. Serum-based biomarkers, such as lactate dehydrogenase, can also reflect tumour burden and are often also correlated with a poor response to immune-checkpoint inhibitors. Other circulating markers (such as circulating free tumour DNA and/or circulating tumour cells) are also attracting research interest as surrogate markers of tumour burden. In this Review, we summarize evidence supporting the utility of tumour burden as a biomarker to guide the use of immune-checkpoint inhibitors. We also describe data and provide perspective on the various tools used for tumour burden assessment, with a particular emphasis on future therapeutic strategies that might address the issue of inferior outcomes among patients with cancer with a high tumour burden.

The PEMDAC phase 2 study of pembrolizumab and entinostat in patients with metastatic uveal melanoma

Preclinical studies have suggested that epigenetic therapy could enhance immunogenicity of cancer cells. We report the results of the PEMDAC phase 2 clinical trial (n = 29; NCT02697630) where the HDAC inhibitor entinostat was combined with the PD-1 inhibitor pembrolizumab in patients with metastatic uveal melanoma (UM). The primary endpoint was objective response rate (ORR), and was met with an ORR of 14%. The clinical benefit rate at 18 weeks was 28%, median progression free survival was 2.1 months and the median overall survival was 13.4 months. Toxicities were manageable, and there were no treatment-related deaths. Objective responses and/or prolonged survival were seen in patients with BAP1 wildtype tumors, and in one patient with an iris melanoma that exhibited a UV signature. Longer survival also correlated with low baseline ctDNA levels or LDH. In conclusion, HDAC inhibition and anti-PD1 immunotherapy results in durable responses in a subset of patients with metastatic UM.Trial registration ClinicalTrials.gov registration number: NCT02697630 (registered 3 March 2016). EudraCT registration number: 2016-002114-50.

Evolution of delayed resistance to immunotherapy in a melanoma responder

Despite initial responses1-3, most melanoma patients develop resistance4 to immune checkpoint blockade (ICB). To understand the evolution of resistance, we studied 37 tumor samples over 9 years from a patient with metastatic melanoma with complete clinical response to ICB followed by delayed recurrence and death. Phylogenetic analysis revealed co-evolution of seven lineages with multiple convergent, but independent resistance-associated alterations. All recurrent tumors emerged from a lineage characterized by loss of chromosome 15q, with post-treatment clones acquiring additional genomic driver events. Deconvolution of bulk RNA sequencing and highly multiplexed immunofluorescence (t-CyCIF) revealed differences in immune composition among different lineages. Imaging revealed a vasculogenic mimicry phenotype in NGFRhi tumor cells with high PD-L1 expression in close proximity to immune cells. Rapid autopsy demonstrated two distinct NGFR spatial patterns with high polarity and proximity to immune cells in subcutaneous tumors versus a diffuse spatial pattern in lung tumors, suggesting different roles of this neural-crest-like program in different tumor microenvironments. Broadly, this study establishes a high-resolution map of the evolutionary dynamics of resistance to ICB, characterizes a de-differentiated neural-crest tumor population in melanoma immunotherapy resistance and describes site-specific differences in tumor-immune interactions via longitudinal analysis of a patient with melanoma with an unusual clinical course.

Current status of ctDNA in precision oncology for hepatocellular carcinoma

The conventional method used to obtain a tumor biopsy for hepatocellular carcinoma (HCC) is invasive and does not evaluate dynamic cancer progression or assess tumor heterogeneity. It is thus imperative to create a novel non-invasive diagnostic technique for improvement in cancer screening, diagnosis, treatment selection, response assessment, and predicting prognosis for HCC. Circulating tumor DNA (ctDNA) is a non-invasive liquid biopsy method that reveals cancer-specific genetic and epigenetic aberrations. Owing to the development of technology in next-generation sequencing and PCR-based assays, the detection and quantification of ctDNA have greatly improved. In this publication, we provide an overview of current technologies used to detect ctDNA, the ctDNA markers utilized, and recent advances regarding the multiple clinical applications in the field of precision medicine for HCC.

Find the Flame: Predictive Biomarkers for Immunotherapy in Melanoma

Immunotherapy has revolutionized the therapeutic landscape of melanoma. In particular, checkpoint inhibition has shown to increase long-term outcome, and, in some cases, it can be virtually curative. However, the absence of clinically validated predictive biomarkers is one of the major causes of unpredictable efficacy of immunotherapy. Indeed, the availability of predictive biomarkers could allow a better stratification of patients, suggesting which type of drugs should be used in a certain clinical context and guiding clinicians in escalating or de-escalating therapy. However, the difficulty in obtaining clinically useful predictive biomarkers reflects the deep complexity of tumor biology. Biomarkers can be classified as tumor-intrinsic biomarkers, microenvironment biomarkers, and systemic biomarkers. Herein we review the available literature to classify and describe predictive biomarkers for checkpoint inhibition in melanoma with the aim of helping clinicians in the decision-making process. We also performed a meta-analysis on the predictive value of PDL-1.

Precision Medicine and Melanoma: Multi-Omics Approaches to Monitoring the Immunotherapy Response

The treatment and management of patients with metastatic melanoma have evolved considerably in the "era" of personalized medicine. Melanoma was one of the first solid tumors to benefit from immunotherapy; life expectancy for patients in advanced stage of disease has improved. However, many progresses have yet to be made considering the (still) high number of patients who do not respond to therapies or who suffer adverse events. In this scenario, precision medicine appears fundamental to direct the most appropriate treatment to the single patient and to guide towards treatment decisions. The recent multi-omics analyses (genomics, transcriptomics, proteomics, metabolomics, radiomics, etc.) and the technological evolution of data interpretation have allowed to identify and understand several processes underlying the biology of cancer; therefore, improving the tumor clinical management. Specifically, these approaches have identified new pharmacological targets and potential biomarkers used to predict the response or adverse events to treatments. In this review, we will analyze and describe the most important omics approaches, by evaluating the methodological aspects and progress in melanoma precision medicine.

The Prognostic Impact of Circulating Tumour DNA in Melanoma Patients Treated with Systemic Therapies-Beyond BRAF Mutant Detection

In this study, we evaluated the predictive value of circulating tumour DNA (ctDNA) to inform therapeutic outcomes in metastatic melanoma patients receiving systemic therapies. We analysed 142 plasma samples from metastatic melanoma patients prior to commencement of systemic therapy: 70 were treated with BRAF/MEK inhibitors and 72 with immunotherapies. Patient-specific droplet digital polymerase chain reaction assays were designed for ctDNA detection. Plasma ctDNA was detected in 56% of patients prior to first-line anti-PD1 and/or anti-CTLA-4 treatment. The detection rate in the immunotherapy cohort was comparably lower than those with BRAF inhibitors (76%, p = 0.0149). Decreasing ctDNA levels within 12 weeks of treatment was strongly concordant with treatment response (Cohen's k = 0.798, p < 0.001) and predictive of longer progression free survival. Notably, a slower kinetic of ctDNA decline was observed in patients treated with immunotherapy compared to those on BRAF/MEK inhibitors. Whole exome sequencing of ctDNA was also conducted in 9 patients commencing anti-PD-1 therapy to derive tumour mutational burden (TMB) and neoepitope load measurements. The results showed a trend of high TMB and neoepitope load in responders compared to non-responders. Overall, our data suggest that changes in ctDNA can serve as an early indicator of outcomes in metastatic melanoma patients treated with systemic therapies and therefore may serve as a tool to guide treatment decisions.

Circulating tumour DNA and melanoma survival: A systematic literature review and meta-analysis

We reviewed and meta-analysed the available evidence (until December 2019) about circulating tumour DNA (ctDNA) levels and melanoma patients survival. We included twenty-six studies (>2000 patients overall), which included mostly stage III-IV cutaneous melanoma patients and differed widely in terms of systemic therapy received and somatic mutations that were searched. Patients with detectable ctDNA before treatment had worse progression-free survival (PFS) (summary hazard ratio (SHR) 2.47, 95 % confidence intervals (CI) 1.85-3.29) and overall survival (OS) (SHR 2.98, 95 % CI 2.26-3.92), with no difference by tumour stage. ctDNA detectability during follow-up was associated with poorer PFS (SHR 4.27, 95 %CI 2.75-6.63) and OS (SHR 3.91, 95 %CI 1.97-7.78); in the latter case, the association was stronger (p = 0.01) for stage IV vs. III melanomas. Between-estimates heterogeneity was low for all pooled estimates. ctDNA is a strong prognostic biomarker for advanced-stage melanoma patients, robust across tumour (e.g. genomic profile) and patients (e.g. systemic therapy) characteristics.

Circulating Tumour DNA in Advanced Melanoma Patients Ceasing PD1 Inhibition in the Absence of Disease Progression

Simple Summary

Immunotherapy is an effective treatment that harnesses the immune system to fight cancer. Drugs such as immune checkpoint inhibitors have demonstrated efficacy in the treatment of advanced melanoma. However, the optimal duration of treatment is not well established. The aim of our retrospective study was to analyse the outcomes of patients who have stopped immunotherapy treatment for advanced melanoma after durable disease control. Furthermore, we assessed circulating tumour DNA (ctDNA), which is shed from the tumour into the bloodstream, to determine its validity as a predictive biomarker of disease progression after treatment was stopped. We demonstrated that stopping treatment after durable disease control results in excellent short- to medium-term prognosis and ctDNA present at the time of stopping treatment is a strong predictor of disease recurrence.

Abstract

Immunotherapy is an important and established treatment option for patients with advanced melanoma. Initial anti-PD1 trials arbitrarily defined a two-year treatment duration, but a shorter treatment duration may be appropriate. In this study, we retrospectively assessed 70 patients who stopped anti-PD1 therapy in the absence of progressive disease (PD) to determine clinical outcomes. In our cohort, the median time on treatment was 11.8 months. Complete response was attained at time of anti-PD1 discontinuation in 61 (87%). After a median follow up of 34.2 months (range: 2–70.8) post discontinuation, 81% remained disease free. Using ddPCR, we determine the utility of circulating tumour DNA (ctDNA) to predict progressive disease after cessation (n = 38). There was a significant association between presence of ctDNA at cessation and disease progression (p = 0.012, Fisher’s exact test) and this conferred a negative and positive predictive value of 0.82 (95% CI: 0.645–0.930) and 0.80 (95% CI 0.284–0.995), respectively. Additionally, dichotomised treatment-free survival in patients with or without ctDNA at cessation was significantly longer in the latter group (p < 0.001, HR: 0.008, 95% CI: 0.001–0.079). Overall, our study confirms that durable disease control can be achieved with cessation of therapy in the absence of disease progression and undetectable ctDNA at cessation was associated with longer treatment-free survival.