Resistance, rebound, and recurrence regrowth patterns in pediatric low-grade glioma treated by MAPK inhibition: A modified Delphi approach to build international consensus-based definitions-International Pediatric Low-Grade Glioma Coalition

Pediatric low-grade glioma (pLGG) is the most common childhood brain tumor group. The natural history, when curative resection is not possible, is one of a chronic disease with periods of tumor stability and episodes of tumor progression. While there is a high overall survival rate, many patients experience significant and potentially lifelong morbidities. The majority of pLGGs have an underlying activation of the RAS/MAPK pathway due to mutational events, leading to the use of molecularly targeted therapies in clinical trials, with recent regulatory approval for the combination of BRAF and MEK inhibition for BRAFV600E mutated pLGG. Despite encouraging activity, tumor regrowth can occur during therapy due to drug resistance, off treatment as tumor recurrence, or as reported in some patients as a rapid rebound growth within 3 months of discontinuing targeted therapy. Definitions of these patterns of regrowth have not been well described in pLGG. For this reason, the International Pediatric Low-Grade Glioma Coalition, a global group of physicians and scientists, formed the Resistance, Rebound, and Recurrence (R3) working group to study resistance, rebound, and recurrence. A modified Delphi approach was undertaken to produce consensus-based definitions and recommendations for regrowth patterns in pLGG with specific reference to targeted therapies.

BRAF inhibitor cessation prior to disease progression in metastatic melanoma: Long-term outcomes

BACKGROUND

BRAF mutant melanoma treated with BRAF ± MEK inhibitor (targeted therapy) has a high response rate; however, most patients progress (PD). Some patients have durable response, but it is unknown whether treatment can be discontinued in these patients. We describe the recurrence risk, progression patterns, response to subsequent treatment, and survival of patients with advanced melanoma who ceased targeted therapy prior to PD.

PATIENTS AND METHODS

Ninety-four patients who ceased targeted therapy without progression were identified retrospectively from 11 centres: 45 were male; 81 V600E; 88 stage IV. Fifty-nine were treated with BRAF + MEK inhibitor, and 35 were treated with BRAF inhibitor alone. Median treatment duration was 29.6 months (range 0.36-77.9). At cessation, 67 were in complete response, 21 in partial response, and 2 stable disease.

RESULTS

After median follow-up from cessation of 42.9 months (range 0.0-88.7), 36 (38%) progressed; median time to progression was 4.7 months (range 0.7-56.9); 30 (83%) were asymptomatic and 7 (19%) had new brain metastases. Progression rates did not differ by best response: 34% for complete response and 43% for partial response (P = 0.65). Treatment duration was strongly associated with risk of progression: Median treatment duration was 18.3 (range 0.85-65.7) months for those who progressed and 34.6 (range 0.36-77.9) months for those who did not (P = 0.0004). Twenty-two received further targeted therapy with 15 (68%) responses.

CONCLUSION

Risk of progression after cessation of targeted therapy is strongly associated with treatment duration. Response to retreatment with targeted therapy is high.

Should Targeted Therapy Be Continued in BRAF-Mutant Melanoma Patients after Complete Remission?

BACKGROUND

Targeted therapy is used to treat patients with a BRAF-mutated metastatic melanoma and is continued until disease progression or severe toxicity. No robust data on the management of patients achieving a complete remission (CR) are available.

MAIN OBJECTIVE

To determine the relapse rate in the first year after targeted therapy discontinuation in patients in CR.

SECONDARY OBJECTIVES

To determine the relapse rates throughout the follow-up and to identify prognostic factors for relapse at 1 year.

METHODS

A retrospective, monocentric observational study was conducted in patients with advanced melanoma included in the RIC-Mel database who discontinued targeted therapy after achieving a CR confirmed by CT scan and PET/CT scan.

RESULTS

Twenty-nine patients were included. Seventeen (58.6%) patients were treated with BRAF inhibitor (BRAFi) alone and 12 (41.4%) with a BRAFi combined with a MEK inhibitor (BRAFi + MEKi). The median treatment duration was 9.7 months. The relapse rates after discontinuation were 69% at 12 months (BRAFi: 70.6%; BRAFi + MEKi: 66.7%) and 76% at 36 months (BRAFi: 76.5%; BRAFi + MEKi: 75%). A non-significant trend towards a higher risk of relapse was found in women (p = 0.1; RR 3.36; 95% CI 0.77-17.07), in patients with an LDH level greater than the upper limits of normal (p = 0.58; RR 2.43; 95% CI 0.10-56.71), and when more than two metastatic sites were involved (p = 0.19; RR 4.6; 95% CI 0.46-46.51). After relapse, targeted therapy was resumed in 17 patients (7 with BRAFi; 10 with BRAFi + MEKi) with a response rate of 53%.

CONCLUSIONS

This real-life study provided long-term data in patients who discontinued targeted therapy after CR. Most patients experienced a relapse in the first year after targeted therapy discontinuation, of whom 50% were in the first 3 months. After targeted therapy resumption, 53% of relapsing patients achieved an objective response. Patients should be followed during the first year after treatment discontinuation. In addition, patients with less than 3 metastatic sites, a baseline LDH level with normal ranges, men, and patients responding rapidly to treatment would be more likely to maintain a CR after treatment discontinuation.

Liquid biopsy and radiological response predict outcomes following discontinuation of targeted therapy in patients with BRAF mutated melanoma

BACKGROUND

Outcomes of patients with metastatic melanoma discontinuing BRAF-targeted therapy for cumulative toxicity after sustained response are unknown.

PATIENTS AND METHODS

This retrospective case series analysis conducted at a single Cancer Center in Italy included patients with BRAF mutated metastatic melanoma treated with a BRAF inhibitor as a single agent or in combination with a MEK inhibitor between June 1, 2011 and January 1, 2020 and interrupting treatment after achieving complete response (CR) or long-lasting partial response (PR - i.e. > 12 months) due to cumulative toxicity.

RESULTS

We included 24 patients with a median treatment duration of 59.4 months (95%CI 55.4-63.4 - range 12-88). CR and PR were achieved in 71% and 29% of patients, respectively. At a median follow-up after treatment discontinuation of 37.8 months (95%CI 33.7-41.9), 12-months progression free survival after discontinuation (dPFS) rate was 70.8% (95%CI 54.8 - 91.6) and 24-months dPFS rate was 58.3% (95%CI 41.6 - 81.8). Baseline patients and tumor characteristics as well as treatment duration and best response did not significantly impact on dPFS. Patients with CR and negative circulating tumor DNA (ctDNA) at time of discontinuation had a significantly improved dPFS compared to patients with either radiological residual disease or ctDNA positivity (P = 0.007). No patient in CR with undetectable ctDNA experienced progression.

CONCLUSION

The risk of progression is high even in patients with sustained sensitivity to BRAF/MEK inhibitors. Integration of liquid biopsy in clinical trials investigating optimal management of patients with sustained sensitivity to BRAF/MEK inhibitors is warranted.

IMPLICATIONS FOR PRACTICE

Outcomes of patients with metastatic melanoma discontinuing BRAF-targeted therapy for cumulative toxicity are unknown. We analyzed patients with sustained responses (median treatment duration 59.4 months). Twelve and 24-months progression free survival following discontinuation were 70.8% and 58.3% respectively. Complete response and negative ctDNA at time of discontinuation are promising prognostic biomarkers in this setting.

Discontinuation of BRAF/MEK-Directed Targeted Therapy after Complete Remission of Metastatic Melanoma-A Retrospective Multicenter ADOReg Study

The advent of BRAF/MEK inhibitors (BRAFi/MEKi) has significantly improved progression-free (PFS) and overall survival (OS) for patients with advanced BRAF-V600-mutant melanoma. Long-term survivors have been identified particularly among patients with a complete response (CR) to BRAF/MEK-directed targeted therapy (TT). However, it remains unclear which patients who achieved a CR maintain a durable response and whether treatment cessation might be a safe option in these patients. Therefore, this study investigated the impact of treatment cessation on the clinical course of patients with a CR upon BRAF/MEK-directed-TT. We retrospectively selected patients with BRAF-V600-mutant advanced non-resectable melanoma who had been treated with BRAFi ± MEKi therapy and achieved a CR upon treatment out of the multicentric skin cancer registry ADOReg. Data on baseline patient characteristics, duration of TT, treatment cessation, tumor progression (TP) and response to second-line treatments were collected and analyzed. Of 461 patients who received BRAF/MEK-directed TT 37 achieved a CR. TP after initial CR was observed in 22 patients (60%) mainly affecting patients who discontinued TT (n = 22/26), whereas all patients with ongoing TT (n = 11) maintained their CR. Accordingly, patients who discontinued TT had a higher risk of TP compared to patients with ongoing treatment (p < 0.001). However, our data also show that patients who received TT for more than 16 months and who discontinued TT for other reasons than TP or toxicity did not have a shorter PFS compared to patients with ongoing treatment. Response rates to second-line treatment being initiated in 21 patients, varied between 27% for immune-checkpoint inhibitors (ICI) and 60% for BRAFi/MEKi rechallenge. In summary, we identified a considerable number of patients who achieved a CR upon BRAF/MEK-directed TT in this contemporary real-world cohort of patients with BRAF-V600-mutant melanoma. Sustained PFS was not restricted to ongoing TT but was also found in patients who discontinued TT.

Clinical Implications of Acquired BRAF Inhibitors Resistance in Melanoma

Understanding the role of mitogen-activated protein kinase (MAPK) pathway-activating mutations in the development and progression of melanoma and their possible use as therapeutic targets has substantially changed the management of this neoplasm, which, until a few years ago, was burdened by severe mortality. However, the presence of numerous intrinsic and extrinsic mechanisms of resistance to BRAF inhibitors compromises the treatment responses’ effectiveness and durability. The strategy of overcoming these resistances by combination therapy has proved successful, with the additional benefit of reducing side effects derived from paradoxical activation of the MAPK pathway. Furthermore, the use of other highly specific inhibitors, intermittent dosing schedules and the association of combination therapy with immune checkpoint inhibitors are promising new therapeutic strategies. However, numerous issues related to dose, tolerability and administration sequence still need to be clarified, as is to be expected from currently ongoing trials. In this review, we describe the clinical results of using BRAF inhibitors in advanced melanoma, with a keen interest in strategies aimed at overcoming resistance.

Stopping targeted therapy for complete responders in advanced BRAF mutant melanoma

BRAF inhibitors revolutionised the management of melanoma patients and although resistance occurs, there is a subgroup of patients who maintain durable disease control. For those cases with durable complete response (CR) it is not clear whether it is safe to cease therapy. Here we identified 13 patients treated with BRAF +/- MEK inhibitors, who cease therapy after prolonged CR (median = 34 months, range 20-74). Recurrence was observed in 3/13 (23%) patients. In the remaining 10 patients with sustained CR off therapy, the median follow up after discontinuation was 19 months (range 8-36). We retrospectively measured ctDNA levels using droplet digital PCR (ddPCR) in longitudinal plasma samples. CtDNA levels were undetectable in 11/13 cases after cessation and remained undetectable in patients in CR (10/13). CtDNA eventually became detectable in 2/3 cases with disease recurrence, but remained undetectable in 1 patient with brain only progression. Our study suggests that consideration could be given to ceasing targeted therapy in the context of prolonged treatment, durable response and no evidence of residual disease as measured by ctDNA.

ESMO consensus conference recommendations on the management of metastatic melanoma: under the auspices of the ESMO Guidelines Committee

The European Society for Medical Oncology (ESMO) held a consensus conference on melanoma on 5-7 September 2019 in Amsterdam, The Netherlands. The conference included a multidisciplinary panel of 32 leading experts in the management of melanoma. The aim of the conference was to develop recommendations on topics that are not covered in detail in the current ESMO Clinical Practice Guideline and where available evidence is either limited or conflicting. The main topics identified for discussion were (i) the management of locoregional disease; (ii) targeted versus immunotherapies in the adjuvant setting; (iii) targeted versus immunotherapies for the first-line treatment of metastatic melanoma; (iv) when to stop immunotherapy or targeted therapy in the metastatic setting; and (v) systemic versus local treatment for brain metastases. The expert panel was divided into five working groups to each address questions relating to one of the five topics outlined above. Relevant scientific literature was reviewed in advance. Recommendations were developed by the working groups and then presented to the entire panel for further discussion and amendment before voting. This manuscript presents the results relating to the management of metastatic melanoma, including findings from the expert panel discussions, consensus recommendations and a summary of evidence supporting each recommendation. All participants approved the final manuscript.