1. Introduction
According to the World Health Organization (WHO), lung cancer is still the leading cause of cancer-related deaths worldwide and the second most common cancer in Europe, after breast cancer [
1]. Recently, the development of immunotherapy based on the theory that the immune system plays a protective role by recognizing cancer cells has led to considerable progress in the treatment of non–small-cell lung cancer (NSCLC) with a substantial reduction in mortality [
2]. Despite the benefits that have been established with immunotherapy in the metastatic setting, there are still many patients that do not benefit from this treatment regardless the PDL1 expression status, indicating the need to identify novel predictive factors [
3,
4]. In addition, spatial and temporal heterogeneity of the solid tumor is the main obstacle for consistency in PDL1 testing [
5]. Currently, PDL1 expression remains a predictive biomarker for response to single-agent immunotherapy, to median progression free survival, to median overall survival and clinical outcome. Besides, the efforts to better identify cancer patients have led to the approvals of targeted therapies for patients with specific oncogenic driver mutations. Checkpoint inhibitors have also been improved for patients without an actionable driver mutation given either as monotherapy or in combination with chemotherapy. However, the prognosis for advanced NSCLC patients remains unsatisfactory, with a median progression-free survival of only 2 to 4 months associated with chemotherapy agents or checkpoint inhibitors [
6]. Predictive and prognostic biomarkers are at need to help physicians determine subgroup of patients who may benefit from specific treatments.
Concerning the targeted therapies, the most prevalent genomic driver event in NSCLC is activating mutations in Kirsten rat sarcoma viral oncogene homologue (KRAS) in about 25 to 30% of non–squamous-cell NSCLCs in Western countries [
7]. The most common KRAS mutation subtype is the G12C mutation, which accounts for approximately 13% of all KRAS mutations in NSCLC [
8]. Other less common KRAS mutation subtypes include G12D, G12V, G13C, and Q61H/L which have been implicated with differences in the prognosis and response to treatment in KRAS positive patients [
9,
10]. KRAS mutations are found with different frequencies in males than in females and vary also according to patient ethnicity [
11] and in specific they are more common in Western versus Asian patients (26% versus 11%) [
12]. In addition, they are more commonly found in patients with a history of smoking (30% versus 11%) [
13]. Furthermore, it has been reported that KRAS mutations are more common in adenocarcinoma (20–40%) and less common in squamous cell carcinoma (<5%) [
14].
Overall, KRAS mutations constitute a distinct NSCLC subset of patients as KRAS mutations where standard of care provides modest clinical benefit. It has also been demonstrated that KRAS mutations are mutually exclusive with other oncogene mutations such as epidermal growth factor receptor (EGFR) mutations [
15]. Several meta-analyses have tried to elucidate the prognostic value of KRAS mutation in patients with advanced NSCLCs, however with inconsistent results [
8,
15,
16]. Thus, there is a need to further clarify the role of KRAS mutations in overall survival of NSCLC patients.
The aim of the current retrospective cohort study was the investigation of the role of KRAS mutational status as predictive biomarker on overall survival (OS) and its relation to PDL1 expression and other clinical characteristics of patients diagnosed with advanced NSCLC after receiving immunotherapy with or without platinum-based chemotherapy.
4. Discussion
As the prevalence of KRAS mutations in lung cancer is high, there has been significant interest in developing targeted therapies that specifically address these mutations. Although preclinical and clinical studies have provided encouraging data, there is a notable variation in treatment outcomes, response duration, and resistance mechanisms [
21]. Such variations may be influenced by specific co-mutations that are present at the time of diagnosis [
22]. Due to this inconsistent response to therapy, the development of effective treatments for lung cancer patients with KRAS mutations remains a challenge. Therefore, there is a need for prognostic biomarkers that can help physicians identify a subgroup of patients who may benefit from certain treatments. To our knowledge, this is the first study conducted in a Greek population that investigated the role of the mutational heterogeneity of KRAS status and its relation to PDL1 expression, as predictive biomarkers in a treated cohort. Our study suggests that the presence of KRAS mutations in advanced NSCLC patients has a poor prognostic value, regardless of their PDL1 expression values, after receiving immunotherapy as first-line treatment.
More specifically, the most significant result in our study was the identification of subgroup of patients negative to KRAS mutations regardless of PDL1 expression values that were found with statistically higher median overall survival when compared to patients with positive KRAS mutation. Our results indicate that KRAS mutational status is a biomarker of poor prognosis. Similarly, in previous studies, KRAS mutational status has been associated with a poorer prognosis in previous studies [
23,
24]. Additionally, in another study, researchers suggested that KRAS mutation was an independent predictor of worse overall survival in patients with lung adenocarcinoma treated with first line pembrolizumab monotherapy [
25]. Besides, in a Danish cohort study, KRAS mutation status was associated with PD-L1 expression in tumors, but not with patient survival [
26]. It has also been reported that the impact of KRAS mutations on prognosis may vary depending on the histologic subtype of NSCLC, the smoking history, the stage of the cancer, and the presence of other genetic mutations [
27]. In the present study, 33% of patients diagnosed with adenocarcinoma were found with positive KRAS mutations whereas 10% in patients diagnosed with squamous cell carcinoma which is in accordance with previous studies reporting that KRAS mutations are more common in adenocarcinoma and less common in squamous cell carcinoma [
14]. Nevertheless, no significant differences were found in patients with positive KRAS results among these two different pathologies, regarding clinical characteristics or survival. However, statistical significance was found in Kaplan-Meier survival curves for patients with negative KRAS status, demonstrating that those diagnosed with adenocarcinoma had better survival prognosis compared to patients with squamous cell carcinoma. Previous studied have already reported that squamous cell carcinoma may be a more malignant type in comparison with adenocarcinoma [
28].
Furthermore, in our study, KRAS G12C was the most frequent KRAS mutation in our cohort of patients and was also the most prevalent in current smokers. Our results are in accordance with other studies [
9,
10,
29]. Concerning immunotherapy treatment, we found no statistically significant differences among patients’ response after 6 months in relation to PDL1 expression and KRAS mutational status. According to some studies, tumors with KRAS mutations may have higher levels of PDL1 expression, suggesting that these tumors may be more responsive to immune checkpoint inhibitors [
30,
31]. In our study, 11 patients (11%) with positive KRAS mutation were found with high values of PDL1 expression (>49%). However, the higher percentage (20%) of NSCLC patients with progression disease after 6 months of immunotherapy treatment with or without chemotherapy was found in patients with positive KRAS mutational status with PDL1 expression <49%. On the contrary, recently, in a small cohort, patients with PDL1 overexpression combined with G12C mutation treated with ICIs as first line of treatment, showed significantly longer progression-free survival [
27]. In addition, 12% of our cohort with positive KRAS result and PDL1 expression <49% were reported with partial response, complete response or standard disease. Previous studies suggest that KRAS-mutant lung cancer patients with low PDL1 expression may still benefit from immune checkpoint inhibitor therapy [
32]. Moreover, the results of meta-analysis confirmed that anti-PDL1 with chemotherapy or without was better than chemotherapy alone, with greater OS benefit for the subgroup with KRAS-mutant NSCLCs than wild-type KRAS tumors [
8]. They suggest that anti-PDL1 therapy could be a reference therapy for evaluating the effectiveness of targeted therapies being developed for KRAS-mutant NSCLC patients, especially the subgroup with the KRAS G12C mutation. Overall, the presence of KRAS mutations may decrease the effectiveness of immunotherapy, regardless of PDL1 expression levels. This information could be useful for clinicians when deciding on the best treatment options for NSCLC patients with KRAS mutations.
One limitation of our study is the size number, to support results for genetic analysis for a population. Another limitation is that no data were available concerning different types of co-mutations that may co-exist with KRAS mutations and may contribute to worse clinical outcomes. Studies have shown that KRAS mutations often co-occur with other genetic alterations in NSCLC, including mutations in TP53 and STK11 or CDKN2A [
22,
33]. As co-occurring mutations may contribute to more aggressive disease and worse outcomes, understanding their occurrence could help clinicians identify patients who require more aggressive treatment strategies. Besides, it is critical to understand the mechanisms of resistance to KRAS G12C inhibitors [
31]. The identification of patients at high risk, could lead to the development of more effective and durable treatment strategies for KRAS-mutant NSCLC.
Recently, sotorasib, formerly AMG 510, a small molecule was approved for 3rd line of treatment in patients with KRAS G12C-mutated NSCLC after previous immunotherapy and/or chemotherapy [
34]. It is important to continue conducting research to better understand the impact of KRAS mutations in different treatment contexts [
33]. At this concept, a study evaluated KRAS mutations in minor clones in patients with lung adenocarcinoma treated with EGFR-TKI, concluding that KRAS mutations might hinder the effectiveness of anti-EGFR therapy [
35]. Furthermore, a Greek study, recently showed that the presence of KRAS mutations resulted in a significantly worse survival among patients receiving platinum-based first line treatment [
36]. Future studies could explore the impact of KRAS mutations on prognosis in NSCLC patients receiving different types of treatments, such as chemotherapy or targeted therapies.
Author Contributions
Author Contributions: Conceptualization, A.C.; Methodology and Laboratory sample analysis, K.D., A.C.; Patient’s Data, K.K., K.P., P.P., and V.B.; Statistical Analysis: K.D. and E.B.; Writing – Original Draft Preparation, TS and K.D.; Writing – Review & Editing, K.D. T.S. and K.P.; Supervision, A.C.; All authors provided critical feedback and helped shape the research, analysis, and manuscript. All authors have read and agreed to the published version of the manuscript.