Management of asynchronous multifocal adult glioblastoma with loss of BRAF^V600E -mutant clonality: a case report

Abstract

Glioblastoma (GBM) classification involves a combination of histological and molecular signatures including IDH1/2 mutation, TERT promoter mutation, and EGFR amplification. Non-canonical mutations such as BRAF^V600E, found in 1–2% of GBMs, activate the MEK-ERK signaling pathway. This mutation can be targeted by small molecule inhibitors, offering therapeutic potential for GBM. In this case report, we describe the management of a 67-year-old male with BRAF^V600E -mutant GBM, who experienced both local clonal and distant non-clonal BRAF^V600E -mutant recurrences. Initial treatment involved surgical resection followed by radiotherapy and temozolomide (TMZ). Subsequent recurrences were managed with re-resection and dabrafenib/trametinib combination therapy. Notably, a new, non-clonal BRAF^V600E -negative tumor developed in a distant location, highlighting the challenge of clonal evolution and resistance in GBM management. The patient’s disease ultimately progressed despite multiple lines of therapy, including targeted inhibition. Identifying mechanisms of resistance and tailoring flexible treatment approaches are essential for advancing outcomes in BRAF^V600E -mutant GBM. This case emphasizes the value of molecular profiling in personalizing treatment for patients with multifocal disease. The evolving nature of these tumors requires persistent clinical monitoring and treatment adjustments based on tissue diagnostics.

Introduction

The current classification of glioblastoma (GBM) relies on a combination of histological and molecular signatures, the latter of which includes an assessment for IDH1/2 mutation, TERT promoter mutation, CDKN2A/B homozygous deletion, and EGFR amplification [1]. GBMs also harbor non-canonical mutations that activate mitogenic signaling pathways. Mutations in V-raf murine viral oncogene homolog B1 (BRAF) - a serine-threonine kinase that activates the MEK-ERK signaling pathway - have been implicated in multiple cancers, including 1–2% of GBMs. The most common BRAF mutation is the substitution of valine for glutamic acid at the 600th amino acid (V600E) [2, 3]. The BRAF^V600E mutation is targetable with FDA-approved small molecule inhibitors [4], and when employed, can improve the survival in appropriately selected patients with GBM [5]. In this report, we present and describe the management of a case of BRAF^V600E mutant GBM with evidence of local clonal and distant non-clonal recurrences.

Case description

A 67-year-old male presented with progressively worsening headaches, confusion, and left-hand tremulousness over 3 months. Brain magnetic resonance imaging (MRI) revealed a 8.6 × 4.8 × 4.3 cm heterogeneously enhancing left parietal tumor with a large cystic component (Fig. 1A). The patient underwent an uncomplicated left parietal craniotomy for resection of this lesion. His perioperative course was unremarkable. His postoperative MRI demonstrated near-total resection of the tumor (Fig. 1A). The histopathology from the resection was consistent with a GBM. Additional immunohistochemical analysis identified the presence of a BRAF^V600E mutation (Fig. 2A; Table 1). A course of concomitant radiotherapy (RT) and temozolomide (TMZ) was initiated.

Three months after the completion of concurrent radiotherapy and TMZ (Fig. 3), a repeat MRI was consistant with disease progression according to RANO 2.0 criteria (Fig. 1B) for which he underwent re-resection [6]. Repeat immunohistochemical analysis demonstrated retention of the BRAF^V600E mutation via weakly positive staining in a focal subset of tumor cells (Fig. 2B). In-house genetic sequencing of the tumor confirmed the presence of a BRAF^V600E mutation (Table 1). Dabrafenib/Trametinib combination therapy was started and continued for over one year with sustained local response to treatment with near resolution of all contrast enhancement (Fig. 1C) – consistent with a partial response according to RANO 2.0 criteria [6]. 14 months after the initiation of the Dabrafenib/Trametinib therapy and 17 months after his initial chemotherapy and radiation (Fig. 3), an interval brain MRI scan demonstrated the presence of a new a 1.3 × 1.4 × 1.6 cm contrast-enhancing mass in his left frontal operculum, distant to the initial site of the tumor (Fig. 1D) [6]. At that time, the left parietal tumor exhibited continued local control on dabrafenib and trametinib therapy (Fig. 1D). An uncomplicated resection of the new left frontal tumor confirmed GBM. Notably, this lesion tested negative for BRAF^V600E mutation upon immunohistochemical analysis (Fig. 2C) and next-generation DNA sequencing (Table 1), indicating potential loss of the BRAF^V600E clonal population. Consequently, dabrafenib/trametinib was discontinued, and concurrent RT and TMZ were reinstated, followed by 3 cycles of adjuvant TMZ (Fig. 3). Between his 2nd and 3rd cycle of TMZ, there was radiographic evidence of disease progression at the previously controlled left parietal resection site as well as pseudoprogression at the left frontal resection site (Fig. 1E). He was initiated on combined TMZ and tovorafenib therapy to attempt to control the progression at both sites. This was well tolerated; however, neither site of disease responded to this line of treatment as evidence by further disease progression at both sites on his subsequent MRI scan (Fig. 1E).

Fig. 1

Pre-operative, Interval, and Post-operative MR Images for Each Surgical Resection

Preoperative (A.i) and postoperative (A.ii) axial T1-weighted post-contrast images from the first resection. Preoperative (B.i) and postoperative (B.ii) axial T1-weighted post-contrast images from the second resection. Red astersik denotes tumor progression at parietal resection site. Axial T1-weighted post-contrast images at the initiation of (C.i) and 6 months after Dabrafenib/Trametinib therapy (C.ii). Preoperative (D.i) and postoperative (D.ii) axial T1-weighted post-contrast MR images from the third resection. Green asterisk denotes tumor progression at frontal site. Axial views of T1-weighted post-contrast images obtained after RT and two cycles of TMZ (E.i) and after one month of combined TMZ and tovorafenib therapy (E.ii). Purple asterisk denotes additional sites of tumor progression.

Fig. 2

BRAF^V600E immunohistochemical analysis for each surgical resection

BRAF^V600E immunohistochemistry with 20x magnification is positive in tumor cells from the first resection (A), weakly positive in a focal subset of tumor cells from the second resection black arrows (B), negative in tumor cells from the third resection (C).

Fig. 3

Timeline

Timeline of surgical and adjuvant therapies for the clinical case [7].

Table 1 Genetic alterations in the left parietal primary, left parietal recurrent and left frontal tumors

Discussion

BRAF mutations are found in up 50% of epithelioid GBMs - a distinct histologic entity associated with worse prognosis compared to traditional GBMs [3]. However, patients with BRAF-mutant GBM often have more durable treatment responses with BRAF inhibition than standard-of-care chemotherapy regimens [8]. Arbour et al. compiled a systematic review of patients treated with BRAF inhibitors for BRAF-mutated gliomas [9]. The progression free survival of the recurrent GBM patients in this review ranged from 3 to 11 months on BRAF inhibitors [9]. While this approach is promising, disease recurrence is still expected and thus it is critical to understand mechanisms for BRAF inhibitor treatment failure in GBM patients.

Kaley et al. studied vemurafenib monotherapy in the VE-BASKET trial, which included recurrent GBM patients who had previously undergone standard of care or other treatment options [10]. The response to vemurafenib monotherapy was variable in the GBM subgroup of six patients, with one patient having a partial radiographic response and two patients achieving stable disease at six months of treatment [10]. The authors hypothesize that this variability is likely due to the significant clonal heterogeneity of these tumors, with monotherapies often selecting for resistant sub-populations. Similarly, the ROAR trial by Wen et al. treated recurrent glioma patients with BRAF^V600E mutations using a combination of dabrafenib and trametinib [11]. They reported objective response rates of 38% in their WHO grade III glioma and 32% in their glioblastoma cohorts. However, the median progression free survival was 3.8 months and 2.8 months respectively suggesting that these responses were not durable [11]. Neither study described whether the treatment failures were local.

Resistance to BRAF inhibitors in glioma is thought to be mediated via various mechanisms, which can emerge adaptively during treatment. One such mechanism involves secondary mutations within the BRAF gene itself. For instance, the BRAF^L514V mutation, identified after progression in a patient treated with dabrafenib, induces ERK signaling and promotes RAF dimer formation, leading to resistance to the inhibitor [12]. Additionally, upregulation of CRAF has been validated as a resistance mechanism in glioma samples, suggesting that alterations in RAF isoforms contribute to treatment failure [13]. Mechanisms such as loss of PTEN or NF1, although tested for and found negative in this patient’s case, are known to confer resistance by maintaining ERK pathway signaling [13]. Furthermore, autophagy has been implicated as an alternative resistance pathway; pharmacologic inhibition of autophagy using chloroquine has shown efficacy in overcoming resistance to BRAF inhibitors, demonstrating the complexity of resistance mechanisms [14].

The case described in this report highlights clonal evolution and selection as potential contributors to disease progression and failure of BRAF-inhibitor therapy in GBM. Similar instances of this have been reported in the literature [10]; however, this report - to the best of our knowledge – may represent the first instance in which this has been identified in two non-contiguous lesions. While our patient did not respond to tovorafenib after progression at the original site of BRAF^V600E mutant disease, the recurrent left parietal disease was not biopsied. This could represent a lack of response to second-line BRAF inhibition; however, a loss of BRAF mutation at this site cannot be excluded. Although this report did not include testing for CBL or RAF upregulation, the presence of such undetected mechanisms at the second site could have contributed to the observed resistance. Understanding the mechanisms of resistance and selecting appropriate, adaptive treatment strategies remain critical for improving outcomes in BRAF-mutated GBM. This case underscores these principles and demonstrates the pivotal role of molecular profiling in tailoring targeted therapies for patients with multifocal lesions. Nonetheless, the findings should be interpreted with an understanding of the limitations inherent to this case, including that while molecular testing was performed, not every potential resistance mechanism was evaluated. The dynamic nature of the tumor in these cases necessitates ongoing clinical evaluation, and adaptive treatment strategies guided by updated tissue diagnosis.