Uterine carcinosarcomas (UCS), also known as mixed malignant Mullerian tumors (MMMT), are a rare histological type of endometrial cancer accounting for <5% of all uterine malignancies and are characterized by a poor prognosis. UCS are biphasic tumors defined by the presence of both carcinomatous and sarcomatous components arising from a single malignant epithelial clone [1]. The majority of UCS harbor a high-grade serous epithelial component demonstrating molecular/genetic characteristics similar to high-grade serous uterine carcinomas (USC) [2]. Consistent with this view, the most common mutated genes in UCS are TP53 (60–97%), FBXW (10–44%), PPP2R1A (11–30%) and HER2 (9–18%) and according to molecular classifications, 73.9%, 5.3%, 7.3%, and 13.5% of UCS harbor P53 mutations, Polymerase epsilon (POLE) mutations, microsatellite instability high (MSI-H), or have a non-specific molecular profile, respectively [[3], [4], [5], [6], [7]]. As expected, the range of epithelial-to-mesenchymal transition (EMT) gene signature scores in UCS was the largest among all tumor types studied via The Cancer Genome Atlas [4]. Traditional treatment of UCS is surgery consisting of hysterectomy, bilateral salpingo-oophorectomy, lymph node assessment, and omentectomy, including aggressive cytoreductive surgery in advanced-stage disease. Due to their high biological aggressiveness, even early stage UCS patients (i.e., stage I) are recommended to receive adjuvant treatment consisting of chemotherapy plus/minus radiation to decrease the risk of recurrence (https://www.nccn.org/guidelines/category_1). The combinations of paclitaxel with carboplatin or paclitaxel with ifosfamide represent the current gold standard adjuvant treatments for UCS [8,9]. However, despite aggressive surgical and adjuvant chemotherapy 5-year survival rates for UCS patients remain poor and accordingly, the development of novel, effective therapies against UCS progressing on chemotherapy remain desperately needed [10].

Our research group as well as others have recently evaluated the genetic landscape of UCS using whole exome sequencing (WES) [1,4]. These comprehensive genetic studies have not only improved our understanding of the distinct pathogenic pathways active in UCS but also identified common activating mutations in genes including KRAS, PTK2, BRAF, MAP2K, and MAP2K1, potentially “druggable” using novel RAF/MEK inhibitors [6]. Indeed, KRAS mutations have been reported in 12–16% of UCS [1,4,11].

Avutometinib is a novel RAF/MEK clamp that induces dominant negative complexes of RAF with MEK and prevents downstream activation of the RAS/MAPK pathway. In preclinical studies, it has been shown to inhibit proliferation of KRAS, NRAS, BRAF, and CRAF mutant cell lines [12,13]. Avutometinib was initially evaluated in a phase I single-center, open-label trial in patients with RAS/RAF-mutant solid tumors and proven to have an acceptable toxicity profile with a twice weekly intermittent dosing schedule. Fifty-one patients with solid tumors were enrolled, eight with gynecologic malignancies; all patients harbored mutations in the RAS/MAPK pathway. Of the 5 evaluable patients with gynecologic malignancies, 3 (60%) had an objective response [14]. Focal Adhesion Kinase (FAK) is a nonreceptor intracellular tyrosine kinase which is known to play a critical role in cancer cell migration, proliferation, and survival and is overexpressed in many cancer types and confers a poor prognosis [15]. The FAK inhibitors defactinib and VS-4718 have shown synergistic anti-tumor activity with avutometinib in multiple cancer models including low-grade serous ovarian cancer (LGSOC), as they block the potential of FAK to function as an adaptive resistance mechanism to RAF/MEK inhibition [15,16]. The FAK inhibitor VS-4718 is used in mouse models as a surrogate for the clinical FAK inhibitor defactinib due to poor pharmacokinetics of defactinib in mice [17]. Clinically, the combination of avutometinib and defactinib is currently being evaluated in a multicenter, randomized, open-label Phase 2 study of patients with recurrent LGSOC (ENGOT-ov60/GOG-3052/RAMP 201; NCT04625270). Interim analysis of Part A demonstrated confirmed ORRs of 45% (13/29; 95% CI: 26%, 64%) and tumor shrinkage in the vast majority of LGSOC patients (86%; 25/29) [18]. Additionally, this combination is now being evaluated in patients with other gynecological cancers (NCT05512208; NCT05787561).

Given the promising clinical activity of avutometinib with the FAK inhibitor defactinib in LGSOC and lack of information regarding activity of this combination in UCS, we analyzed the mutational signatures by WES of 5 recently established and characterized primary UCS cell lines and evaluated the preclinical activity of avutometinib ± FAK inhibitor against UCS cell lines and xenografts [19]. We provide the first experimental evidence to demonstrate that uterine CS harboring RAS/MAPK pathway alterations may be sensitive to RAF/MEK and FAK inhibitors both in vitro as well as in vivo.