BRAF and MEK Inhibitor Treatment for Metastatic Undifferentiated Sarcoma of the Spermatic Cord with BRAF V600E Mutation

Soft tissue sarcoma (STS) is a rare mesenchymal neoplasm with heterogeneous histological subtypes [1]. STS can occur everywhere in the body, including the head, neck, extremities, internal organs, and reproductive organs. Chemotherapy is the primary treatment option for recurrent and metastatic STS [2]. Doxorubicin, with or without add-on ifosfamide, is widely used to treat STS. However, the response rate is less than 20% [3]. Therefore, an urgent need exists to develop additional treatment options for patients with STS. In response to this need, the use of comprehensive genomic profiling tests in solid cancers has led to a better understanding of molecular mechanisms underlying the pathogenesis of cancers and to the discovery of treatment-targeted molecules. Indeed, targeted therapies based on genomic profiling tests have been accepted in clinical practice and resulted in unprecedented outcome improvement in the treatment of some solid cancers, such as non-small-cell lung cancer and biliary tract cancer [4, 5]. Generally, targeted therapy has a better tolerated toxicity profile than conventional chemotherapy [4]. A number of clinical trials are being conducted aimed at evaluating targeted therapies. The BRAF V600E mutation is a promising therapeutic target because BRAF V600E can potently drive oncogenic cell proliferation. In addition, specific BRAF inhibitors are currently available. Oncogenic BRAF mutations occur in various malignancies, including malignant melanoma (50%), thyroid cancer (30%–50%), and colorectal cancer (10%) [6]. However, only a few cases of STS with BRAF mutation have been described [7]. Studies examining treatment outcomes with the use of specific BRAF inhibitors are scarce [8]. The significance of BRAF mutations in patients with STS remains unclear. This report describes a case of BRAF-mutated undifferentiated sarcoma successfully treated with BRAF and MEK inhibitors and suggests the potential of the BRAF V600E mutation as a therapeutic target in patients with STS.

In December 2020, an 18-year-old Japanese man presented with swelling of the right scrotum due to an approximately 5-cm tumor in the spermatic cord (Fig. 1a). The patient had no previous history of illness or familial history of cancer. Chest radiography revealed multiple lung metastases (Fig. 1b). In addition, computed tomography (CT) revealed multiple metastases to the bones in the spine, ribs, and pelvis. Bone scintigraphy revealed tracer uptake in the same bone lesions (Fig. 1c). In January 2021, he developed paraparesis due to spinal cord compression at the 12th thoracic vertebra (Fig. 1d).

The tumor of the spermatic cord was resected at the Department of Urology. Pathologically, the resected tumor was composed of proliferating large polygonal cells with focal desmin-positive rhabdoid cells. Venous invasion was prominent, and the mitotic figure count was at least 7–8 per 1 high-power field. Immunohistochemically, the cells were negative for AE1/AE3, S100, CDK4, MDM2, CD99, and NKX3.1. The Ki-67 index was 60–70%. No gene fusions involving EWS, CHOP, FUS, FKHR, or MDM2 were detected. Based on the abovementioned findings, the tumor was diagnosed as a high-grade undifferentiated sarcoma of the spermatic cord (Fig. 2). The patient was referred to our department. He received steroids and urgent radiotherapy to the thoracic and lumbar spines consisting of 25 Gy for each lesion. The patient also underwent chemotherapy with doxorubicin and ifosfamide. He developed severe anorexia, neutropenia, febrile neutropenia, and hematuria. These treatment-related adverse events led to a reduction in the chemotherapy dose. He had received four cycles of doxorubicin and ifosfamide therapy until May 2021. A CT scan showed tumor shrinkage in the lung metastasis (Fig. 3a, b). However, as those adverse events recurred even at reduced doses, it was difficult to continue the same chemotherapy regimen.

During chemotherapy, the resected tumor tissue was examined using a comprehensive genomic profiling test (FoundationOne® CDx, FOUNDATION MEDICINE, INC., MA, USA). The BRAF V600E mutation was detected (Table 1). A prospective trial of patient-proposed healthcare services with multiple targeted agents based on the results of gene profiling by multigene panel testing (NCCH1901, jRCTs031190104) is being conducted for patients who have no available clinical trials, even though the test showed actionable mutations, in 12 designated core hospitals for cancer genomic medicine in Japan. In June 2021, according to the trial protocol, the patient started combination therapy with the BRAF inhibitor dabrafenib (300 mg twice a day) and the MEK inhibitor trametinib (2 mg once a day). Both drugs were provided by Novartis Pharma K.K. (Tokyo, Japan).

Six days after starting the combination therapy, the patient developed grade 2 anorexia and fatigue. Both drugs were withheld for 8 days and restarted with a reduced dose of dabrafenib, 200 mg twice daily, and trametinib, 1.5 mg once daily. Two weeks later, the patient developed a fever of 39°C, exanthema of the trunk and extremities, and grade 2 leukocytopenia. No clinical signs of infection were observed. Both drugs were discontinued. The patient’s condition and white blood cell count recovered smoothly. After 8 days, both drugs were resumed. The dose of dabrafenib was further reduced to 100 mg twice daily. In September 2021, a CT scan revealed regression of the lung metastasis and no deterioration of the bone metastasis (Fig. 3c). Since then, both drugs were continued without worsening adverse events. The patient regained the ability to ambulate with the assistance of a stick.

In December 2021, the patient complained of right-sided chest pain. A CT scan showed a newly emerged right pleural dissemination despite further regression of lung metastasis (Fig. 3d). Combination therapy was determined to be refractory, and chemotherapy with doxorubicin and ifosfamide was resumed. In February 2021, after an additional two cycles of chemotherapy, the patient developed diplopia and bilateral lower limb paralysis. Magnetic resonance imaging revealed multiple meningeal disseminations. Palliative radiation to the brain and thoracic and lumbar spinal cord was conducted. In March 2022, a liquid genomic profiling test was performed using the Guardant360® (Guardant Health, Inc. CA, USA). Only the BRAF V600E mutation was detected without additional gene mutations (Table 1). Approximately 1 month later, the patient died of respiratory failure due to the progression of pleural dissemination.

The frequency of BRAF gene mutations in patients with sarcoma is 0–9% [7, 9]. As sarcoma is a rare type of cancer, the number of patients with BRAF-mutated sarcomas is extremely small. The presence of BRAF mutations and treatment outcomes with BRAF-targeted therapy have been reported in only a few cases of different types of sarcomas [8]. The significance of BRAF mutations differs among specific cancer types [10]. Because STS includes various histological subtypes, its significance would also differ among the histological subtypes. Thus, case reports describing the relationships between each STS subtype and BRAF mutation carrier status are meaningful. This case report shows that the BRAF V600E mutation could be a potential therapeutic target for undifferentiated STS.

BRAF-targeted therapy has been developed for cutaneous melanoma associated with the BRAF V600E mutation but not for mucosal melanoma [11]. BRAF inhibitor monotherapy is vulnerable to various resistance mechanisms. Combination therapies have been investigated to circumvent resistance. Based on this concept, the combination of BRAF and MEK inhibitors has shown to be more effective and safer than BRAF inhibitor monotherapy in patients with melanoma [12]. In this case, dabrafenib and trametinib were used as part of a prospective trial of NCCH1901. The progression-free survival time of combination therapy with dabrafenib and trametinib was 6.5 months. The combination therapy induced adverse events such as anorexia, fatigue, pyrexia, exanthema, and leukocytopenia, which have already been reported [13]. However, these adverse effects were less severe than those induced by doxorubicin-based chemotherapy. Furthermore, combination therapy did not require hospitalization, which certainly benefited the patient and family.

Acquired resistance to the combination therapy also developed in this case, showing that, like melanoma, BRAF-targeted combination therapy could be resistant even in STS. To identify the genomic mechanisms of acquired resistance to BRAF and MEK inhibitors, circulating tumor DNA analysis of plasma samples after tumor progression was performed using Guardant360® CDx. Several mechanisms of BRAF inhibitor resistance have been proposed [7]. The major one is the paradoxical activation of the RAS-RAF-MAPK pathway caused by secondary mutations of BRAF or RAS, amplification of RAS, and overexpression of EGFR [7, 14]. Another is the activation of alternative pathways, such as the PI3K-AKT pathway [7]. Liquid biopsy analysis provides real-time information on tumor heterogeneity [15]. Therefore, it is sometimes used to identify resistance mechanisms. No acquired gene alterations other than BRAF V600E were detected in this case. Sub-clonal groups with BRAF mutations thus remained, and other alterations that could not be detected were likely acquired. Guardant360® CDx detects mutations and amplification in 74 and 18 genes, respectively, including most of the BRAF inhibitor resistance-related gene alterations mentioned above. However, the number of gene alterations that can be detected by Guardant360® CDx is only about one-third of those detectable by FoundationOne® CDx. Other minor gene mutations or amplifications related to resistance mechanisms may not be detected in this liquid analysis. There are still several problems associated with liquid biopsy analysis. Liquid biopsy analysis is performed by several different techniques which reduce its reproducibility, and it may provide false negatives when circulating tumor DNA or allele frequency of genetic alterations is low [4]. Identifying the mechanism of resistance in individual cases may not be easy, even with liquid biopsy analysis. In this case, the resistance mechanism may be more complicated than that for BRAF inhibitors because resistance emerged against the combination of BRAF and MEK inhibitors treatment.

Another concern is the heterogeneous response to BRAF-targeted treatment. The resected tumor was histologically heterogeneous, as shown in Figure 2. BRAF mutation may have also been biased in the tumor tissue. We could not detect the relationship between histological features and BRAF mutation. The uneven distribution of BRAF mutation may have led to heterogeneous treatment responses and resistance to the targeted therapy.

The increasing use of comprehensive genomic profiling tests is expected to accumulate findings on molecular targets, especially in rare cancers. In addition, it is hoped that optimized and improved use of liquid biopsy analysis will efficiently reveal resistance mechanisms to the targeted therapy in individual cases.

We reported that a patient with BRAF V600E-mutated undifferentiated sarcoma was successfully treated with a combination of BRAF and MEK inhibitors. A comprehensive genomic profiling test led to the use of molecularly targeted drugs and brought clinical benefits that would not otherwise be considered. This report shows that the BRAF V600E mutation may be a promising therapeutic target and that resistance to targeted therapy could also occur in STS.

We thank Noriko Takenaga for clinical trial coordination. We express sincere gratitude to the patient and his family.

The prospective study (NCCH1901) and this case report were approved by the Ethics Committee of Tohoku University Graduate School of Medicine (approval numbers 2019-30-01 and 25514, respectively). Written informed consent was obtained from the patient’s next of kin for publication of the details of their medical case and any accompanying images.

Chikashi Ishioka was funded by the Tokyo Cooperative Oncology Group and obtained financial support from Chugai Pharmaceutical, Ono Pharmaceutical, MSD, Pfizer, AstraZeneca, Bristol-Myers Squibb, Janssen Pharmaceutical, Taiho Pharmaceutical, Daiichi Sankyo Company, Limited, and Takeda Pharmaceutical; it is a representative of the Tohoku Clinical Oncology Research and Education Society, a specified nonprofit corporation. Masanobu Takahashi received research funding from Ono Pharmaceutical Co., Ltd. Kenichi Nakamura received research funding from the Chugai Pharmaceutical and Taiho Pharmaceutical company. The other authors have no conflicts of interest to declare.

There is no funding source relevant to this report.

Ken Saijo conducted this study. Ken Saijo, Hiroo Imai, Hiromichi Katayama, Yuki Kasahara, Kota Ouchi, Keigo Komine, Hidekazu Shirota, and Masanobu Takahashi treated the patients. Fumiyoshi Fujishima performed the histopathological analysis. Kenichi Nakamura is a member of the coordinating office of the NCCH1901. Chikashi Ishioka reviewed the study.

All data in this case are included in this article. Further inquiries can be directed to the corresponding authors.