Clinical Predictors of Survival in Patients With BRAFV600-Mutated Metastatic Melanoma Treated With Combined BRAF and MEK Inhibitors After Immune Checkpoint Inhibitors

Abstract Prospective and between trial comparisons indicate that first-line treatment with immune checkpoint inhibitors improves survival outcomes compared to first-line therapy with combined BRAF and MEK inhibitors in metastatic melanoma containing BRAFV600E/K mutations. Long-term outcomes for BRAF/MEK inhibition after progression on immunotherapy have not been reported. Moreover, clinical variables associated with outcome from treatment with combined BRAF/MEK inhibition were previously identified in the first-line setting but have not been investigated when targeted therapies are administered after progression on immune therapy. We performed a retrospective single institution analysis of 40 metastatic melanoma patients receiving combined BRAF/MEK inhibitors after progression on an anti-PD-1 or ipilimumab plus nivolumab to assess response rate by RECIST 1.1, progression-free and overall survival (PFS and OS). Pretreatment clinical variables were analyzed for association with OS. Ipilimumab/nivolumab was the first-line immunotherapy regimen in 39 patients (97.5%), and BRAFV600E/K mutations were present in 33 (83%) and 7 (17%) patients, respectively. The median OS from start of BRAF/MEK inhibitors was 20.3 months (1.73-106.4+, 95% CI of median 13.3-30.7). Clinical characteristics associated with worse survival prior to starting BRAF/MEK inhibitors included age > 60 years (median OS 14 vs. 28 months; HR 2.5; 95% CI 0.91-6.87, P = .023), ECOG-PS > 2 (median OS 7 vs. 33 months; HR 2.89; 95% CI 0.78-10.76, P = .018), and presence of bone metastases (median OS 9 vs. 52 months; HR 3.17; 95% CI 1.33-7.54, P = .002). These associations with shorter survival maintained their significance on multivariate analysis. If confirmed in larger cohorts, the identified prognostic variables can be used for stratification of patients in future randomized trials.


Background
][10][11] Both checkpoint inhibitor immunotherapy and targeted therapy prolong progression-free and overall survival compared with chemotherapy in metastatic melanoma.

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The Oncologist, 2024, Vol. 29, No. 4   In patients with BRAF V600 mutations, prior phase II and phase III studies had shown that first-line treatment with anti-PD-1 alone or ipilimumab plus nivolumab (ipi/nivo) produced long-term objective responses that were maintained despite discontinuation of treatment.Moreover, cross-trial comparisons suggested that survival outcomes were better with first-line immune checkpoint inhibitors compared to first-line therapy with BRAF/MEKi. 12,13The latter observations were confirmed by the DREAMseq trial, which randomized 265 patients with newly diagnosed metastatic melanoma to the sequence of ipi/nivo followed upon disease progression by dabrafenib plus trametinib versus the inverse sequence, and showed that the 2-year overall survival (OS) rate was superior for those starting with ipi/nivo (71.8% vs. 51.5%;log-rank P = .010). 12,14dministration of BRAF/MEKi following disease progression on immune checkpoint inhibitors is a standard of care, although limited prospective data have been collected.6][17][18][19][20][21][22][23] Long-term clinical outcomes for patients receiving BRAF/MEKi after progression on immune therapy have not been fully described, and clinical predictors of long-term response and survival are not known and may be different than those already described for patients receiving targeted therapy as the first-line therapy for metastatic disease.Therefore, we performed a retrospective analysis of patients receiving BRAF/MEKi after progression on one or more lines of immune checkpoint inhibitor therapy to assess objective response rates, PFS and OS, and clinical variables associated with survival.

Patients
We retrospectively identified patients with metastatic melanoma treated at our institution from 2011 to 2020 who met the following inclusion criteria: BRAF V600E/K mutation; had not received BRAF/MEKi before immune checkpoint inhibitors; and received ipi/nivo or anti-PD-1 (alone or in combination with other immune therapy agents) followed by BRAF/ MEKi upon progression.We included patients who had received multiple lines of immune checkpoint inhibitors provided that at least one regimen of immune checkpoint inhibitors was administered before BRAF/MEKi.Patients were also included if the BRAF-MEKi regimen was combined with immune checkpoint inhibitors.There was no restriction on therapies administered upon progression on the initial BRAF/ MEKi regimen.

Clinical Characteristics and Endpoints
The following clinical characteristics prior to initiation of BRAF/MEKi were analyzed for potential association with treatment outcome: age, sex, type of BRAF mutation, LDH, ECOG performance status, sites of metastases, prior toxicity from immunotherapy, disease response to prior immunotherapy, duration of treatment on checkpoint inhibitor immunotherapy (>6 months versus < 6 months), and use of immunotherapy in addition to or upon progression on BRAF/MEKi.Clinical response to therapy was categorized as complete (CR), partial (PR), stable disease [SD] for more than 6 months, or progression of disease (PD) using RECIST 1.1 criteria, and outcome was analyzed by grouping CR + PR + SD > 6 months versus PD.An additional category of mixed response to immune checkpoint inhibitors (any site of tumor regression despite overall PD by RECIST 1.1 criteria) was also explored, and outcome was analyzed by grouping PD without mixed response versus CR/PR/SD > 6 months/PD with mixed response.Overall safety was assessed as adverse events of any grade occurring in more than 5% of patients per NCI CTCAEv5.Progression-free survival (PFS) and OS were calculated from the start date of BRAF/MEKi.

Statistical Analyses
Clinical data were analyzed by descriptive statistics.Survival (PFS and OS) was analyzed by Cox regression and Kaplan-Meier method.Univariate analysis was calculated with logrank (Mantel-Cox test) and multivariate analysis with Cox proportional hazards regression.
We analyzed 2 additional subgroups of patients with exceptional outcomes as listed in Supplementary Table S1.The first subgroup included patients who were alive for ≥4 years from start of BRAF/MEKi (n = 8/40, 20%) and the second subgroup included patients whose disease did not progress despite stopping BRAF/MEKi due to toxicity or patient choice and were still alive at last follow-up (n = 4/40, 10%).Two out of 4 of the latter patients from the second subgroup had follow-up ≥4 years and are included among the 8 patients in the first subgroup.The clinical characteristics of the ≥4 years long-term survivors were similar to the overall population.For these 8 long-term survivors, the median duration of first-line immunotherapy was 3.5 months (0.5-42.8 months) and all patients had PD as best response to immunotherapy.Five of the 8 were considered to have had mixed response to immune checkpoint inhibitors by treating physicians based on clinical and radiological findings.All had BRAF V600E mutations, and the median duration of second-line BRAF/MEKi was 29.7 months (5.4-55.1 months).Seven had best response of PR to BRAF/MEKi.All but one received immune checkpoint inhibition in addition to or upon progression on BRAF/ MEKi.
From the second subgroup of 4 patients who stopped BRAF/MEKi due to toxicity or patient choice but maintained disease control without further therapy and remained alive at last follow up, all started with ipi/nivo and median duration of first-line immunotherapy was 25 months (16-42 months).Two had PR as best response to immunotherapy while the remaining 2 had PD by RECIST criteria, but with a mixed response.Median duration of BRAF/MEKi therapy was 3.5 months (0.5-16 months) and best response to BRAF/MEKi was PR in 3 and CR in one.One patient received concomitant immune checkpoint inhibition with the BRAF/MEKi regimen.

Discussion
This was a retrospective study assessing the clinical activity, outcomes, and potential clinical factors associated with survival among patients with BRAF V600 -mutated metastatic melanoma treated with BRAF/MEKi after disease progression on immune checkpoint inhibition.The median follow-up of 33 months in our cohort also provided the first opportunity to assess the potential long-term benefit of targeted therapy as administered in a standard of care setting to patients no longer responsive or resistant to doublet immune checkpoint therapy.
Limited prospective data are available for patients who received BRAF/MEKi after progression on immune checkpoint inhibitors, particularly combined ipilimumab plus nivolumab.At the time of publication of the DreamSEQ trial, 44 patients developed disease progression from firstline therapy with ipilimumab plus nivolumab, and only 21 of the latter were registered to step 2 of the study for treatment with second-line BRAF/MEKi. 12Response data were not provided for second-line targeted therapy.In the SECOMBIT trial, 38 patients receiving first-line treatment with ipilimumab + nivolumab received BRAF/MEKi at the time of progression. 13The objective response rate to second-line BRAF/ MEKi was 57.9%, similar to the response rate of 75% observed in our cohort of 40 patients.However, at the time of publication, the SECOMBIT trial did not report duration of response, progression-free or overall survival from initiation of second-line targeted therapy.
We observed that treatment with BRAF/MEKi following progression on immune therapy, including at least one regimen of ipilimumab plus nivolumab, is associated with a 2-year survival of 41.5%, and a 4-year survival rate of 20%.Ten percent of our cohort were able to discontinue BRAF/ MEKi treatment without subsequent disease recurrence.This observed level of activity is indicative of meaningful clinical benefit in at least a subset of patients.The potential for long-term survival with second-line BRAF/MEKi should be considered by patients and physicians when choosing other potential treatment options in this setting including clinical trials or, if approved in the future, adoptive cell therapy with tumor-infiltrating lymphocytes (TIL). 24Nevertheless, the 2-year PFS rate was only 17.5%, clearly indicating the need to develop more effective therapies.
Our data showed that age of 60 years or older, ECOG-PS 3-4, and presence of bone metastases were independently associated with worse survival outcomes as per multivariate analysis.Clinical variables associated with worse outcome post-immune checkpoint inhibitors appeared to be different from those identified in a large pooled 3-year analysis of BRAF inhibitor-naïve patients treated with dabrafenib plus trametinib across phase II (BRF113220, part C) and phase III (COMBI-d, COMBI-v) registration trials.In the latter analyses, baseline LDH and number of organ sites with metastases were strongly associated with worse PFS and OS, and the baseline sum of lesion diameters was identified as a predictor of progression. 18,20he DREAMseq trial explored prognostic features such as age (<40, 40-60, >60), ECOG-PS (0 or 1), sex, type of BRAF mutation, LDH, M stage (<M1c or M1c), and a combination of favorable features (ECOG-PS 0 plus normal LDH and <M1c) and concluded that in all of these subtypes, the strategy of starting with ipi/nivo followed by BRAF/MEKi was numerically associated with improved survival. 12,14There is as of yet no reported results from this study on features of long-term survivors from the start of BRAF-MEKi in the second-line setting.
Despite progression on immunotherapy, a subset of patients receiving BRAF/MEKi have prolonged OS, including some that maintain durable responses even after discontinuing BRAF/MEKi.6][27] We also hypothesized that patients demonstrating tumor regression from prior immune therapy, despite ultimate overall disease progression, may have better outcomes from second-line targeted therapy.In addition to reducing tumor burden, BRAF/MEKi potentially modulate the immunosuppressive tumor microenvironment including antigen presentation, secretion of cytokines, and the ratio of suppressive versus effector tumor-infiltrating lymphocytes in BRAF V600 -mutated tumors. 25,28,29We did not find that adverse events were associated with better survival, including toxicity from prior immunotherapy, or toxicity during BRAF/ MEKi treatment.There was also no association of OS with length of time on immunotherapy prior to BRAF/MEKi, prior tumor regression from immune therapy, or use of immune e510

Table 3 .
Multivariable analysis using Cox proportional hazards regression