A review of trials investigating ctDNA-guided adjuvant treatment of solid tumors: The importance of trial design.

Circulating tumor DNA (ctDNA) holds promise as a biomarker for guiding adjuvant treatment decisions in solid tumors. This review systematically assembles ongoing and published trials investigating ctDNA-directed adjuvant treatment strategies. A total of 57 phase II/III trials focusing on ctDNA in minimal residual disease (MRD) detection were identified, with a notable increase in initiation over recent years. Most trials target stage II or III colon/colorectal cancer, followed by breast cancer and non-small cell lung cancer. Trial methodologies vary, with some randomizing ctDNA-positive patients between standard-of-care (SoC) treatment and intensified regimens, while others aim to de-escalate therapy in ctDNA-negative patients. Challenges in trial design include the need for randomized controlled trials to establish clinical utility for ctDNA, ensuring adherence to standard treatment in control arms, and addressing the ethical dilemma of withholding treatment in high-risk ctDNA-positive patients. Longitudinal ctDNA surveillance emerges as a strategy to improve sensitivity for recurrence, particularly in less proliferative tumor types. However, ctDNA as longitudinal marker is often not validated yet. Ultimately, designing effective ctDNA interventional trials requires careful consideration of feasibility, meaningful outcomes, and potential impact on patient care.

Comprehensive characterization of circulating tumor cells and cell-free DNA in patients with metastatic melanoma.

Advances in therapeutic approaches for melanoma urge the need for biomarkers that can identify patients at risk for recurrence and to guide treatment. The potential use of liquid biopsies in identifying biomarkers is increasingly being recognized. Here, we present a head-to-head comparison of several techniques to analyze circulating tumor cells (CTCs) and cell-free DNA (cfDNA) in 20 patients with metastatic melanoma. In this study, we investigated whether diagnostic leukapheresis (DLA) combined with multimarker flow cytometry (FCM) increased the detection of CTCs in blood compared to the CellSearch platform. Additionally, we characterized cfDNA at the level of somatic mutations, extent of aneuploidy and genome-wide DNA methylation. Both CTCs and cfDNA measures were compared to tumor markers and extracranial tumor burden on radiological imaging. Compared to the CellSearch method applied on peripheral blood, DLA combined with FCM increased the proportion of patients with detectable CTCs from 35% to 70% (P = 0.06). However, the median percentage of cells that could be recovered by the DLA procedure was 29%. Alternatively, cfDNA mutation and methylation analysis detected tumor load in the majority of patients (90% and 93% of samples successfully analyzed, respectively). The aneuploidy score was positive in 35% of all patients. From all tumor measurements in blood, lactate dehydrogenase (LDH) levels were significantly correlated to variant allele frequency (P = 0.004). Furthermore, the presence of CTCs in DLA was associated with tumor burden (P < 0.001), whereas the presence of CTCs in peripheral blood was associated with number of lesions on radiological imaging (P < 0.001). In conclusion, DLA tended to increase the proportion of patients with detectable CTCs but was also associated with low recovery. Both cfDNA and CTCs were correlated with clinical parameters such as LDH levels and extracranial tumor burden.

Trastuzumab and first-line taxane chemotherapy in metastatic breast cancer patients with a HER2-negative tumor and HER2-positive circulating tumor cells: a phase II trial.

PURPOSE: HER2 overexpressing circulating tumor cells (CTCs) are observed in up to 25% of HER2-negative metastatic breast cancer patients. Since targeted anti-HER2 therapy has drastically improved clinical outcomes of patients with HER2-positive breast cancer, we hypothesized that patients with HER2 overexpressing CTCs might benefit from the addition of trastuzumab to chemotherapy. METHODS: In this single-arm, phase II trial, patients with HER2-positive CTCs received trastuzumab as addition to first-line treatment with taxane chemotherapy. Patients with detectable CTCs but without HER2 overexpression that received taxane chemotherapy only, were used as control group. The primary outcome measure was progression-free rate at 6 months (PFR6), with a target of 80%. In November 2022, the study was terminated early due to slow patient accrual. RESULTS: 63 patients were screened, of which eight patients had HER2-positive CTCs and were treated with trastuzumab. The median number of CTCs was 15 per 7.5 ml of blood (range 1-131) in patients with HER2-positive CTCs, compared to median 5 (range 1-1047) in the control group. PFR6 was 50% in the trastuzumab group and 54% in the taxane monotherapy group, with no significant difference in median PFS (8 versus 9 months, p = 0.51). CONCLUSION: No clinical benefit of trastuzumab was observed, although this study was performed in a limited number of patients. Additionally, we observed a strong correlation between the number of evaluable CTCs and the presence of HER2-positive CTCs. We argue that randomized studies investigating agents that are proven to be solely effective in the HER2-positive patient group in patients with HER2-positive CTCs and HER2-negative tissue are currently infeasible. Several factors contribute to this impracticality, including the need for more stringent thresholds, and the rapidly evolving landscape of cancer treatments.