Multiple primary lung cancer tumors with diversified genetic mutations-complications in choosing therapeutic options

Patients diagnosed with primary lung cancer may be diagnosed with more than one lesion based on diagnostic scans. A simultaneous or consecutive occurrence of two or more primary lung cancers in the lung of the same patient is defined as multiple primary lung cancer (MPLC). If at least two primary lung cancer tumors coexist simultaneously in the ipsilateral or contralateral lung within a 6-month timeframe, it is a synchronous multiple primary lung cancer (sMPLC)[1, 2]. On the other hand, metachronous (mMPLC) is when the second primary is diagnosed more than six months after primary cancer.

Currently, the diagnosis of MPLC follows the eighth edition of the American Joint Commission on Cancer (AJCC) staging manual. It is based on clinical, histopathological, and molecular diagnoses of lung tumors[3, 4]. Unlike MPLC, multiple lesions can also be derived from the same tumor. This is defined as intrapulmonary metastases (IPM). Difficulty in diagnosis occurs when multiple tumors are histologically similar, making it hard to distinguish MPLC from metastases. This can be due to the size of the secondary tumors, the need for multiple biopsies, the feasibility of biopsy based on the location and size of the tumor, and the heterogeneity of tumor markers.

In regards to treatment, there are multiple modalities that can be utilized in this patient population. Localized therapy is always preferred, including surgery and/or radiation or chemoradiation. Depending on the location and number of tumors, resectability and/or radiation may not be feasible. For those patients, systemic therapy is the current mainstay of treatment. Molecular markers can provide better options for treating MPLC, including an ability to distinguish from IPM. Next-generation sequencing (NGS) is used to identify the molecular biomarkers that can determine the relationship of multiple lung lesions and can be targeted with medication(s). Our knowledge and treatment armamentarium of oncogenic driver mutations is ever-evolving. The current mutations that have FDA approved treatments for non-small cell lung cancer are epidermal growth factor receptors (EGFR), Kristen rat sarcoma (KRAS), anaplastic lymphoma kinase (ALK), mesenchymal-epithelial transition factor receptor (MET), rearranged during transfection (RET), ROS1, and v-raf murine sarcoma viral oncogene homolog B1 (BRAF), and neurotrophic tyrosine receptor kinase (NTRK) (NCCN guidelines Version 3.2022). These mutations indicate tumors of different clonal origins. However, shared constitutional genetic background and environmental exposure may result in multiple identical lung tumors with EGFR and KRAS mutations. Thus, evaluating only a few mutations may not help distinguish different tumor types [5]. A study was conducted by Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) large-scale NGS assay to determine the mutations in a pair of multiple lung cancer tumors [6]. The idea is to identify non-overlapping mutations in a pair of MPLCs to distinguish them from other types of lung tumors. Why are such detailed analyses critical? Because treatment options for MPLC are different from other types of lung tumors. A surgical approach may result in a poor survival rate of lung cancer patients if diagnosis methods do not distinguish MPLC from intrapulmonary metastasis (IM).

Surgical resection remains the first choice for the treatment of MPLCs; however, it is essential to consider the patient’s general health and pulmonary reserve. Yu. et al. [7] reported that patients undergoing sublobar resection or lobectomy did not significantly differ in 5-year overall survival. However, Ishikawa et al. [8] found that in patients with sMPLC, sublobar resection is a significant independent predictor of poor outcomes indicating a negative impact on curability [9, 10]. Other therapeutic options in patients who are not surgical candidates include stereotactic body radiation therapy and local ablation.

Currently, osimertinib, a third-generation EGFR inhibitor, is the only medication approved for use after lung cancer resection based on the ADAURA study [11]. However, other literature exists utilizing more than one tyrosine kinase inhibitor (TKI) to target multiple pathways in those who are not candidates for surgery. Combination therapy with TKIs in the metastatic setting, such as osimertinib and alectinib, was effective and tolerable in a patients with MPLCs with a distinct molecular profile [12]. However, these targeted therapies for MPLC are challenging since one tumor harboring particular mutations may not represent other lesions. This may result in the development of further resistant mutations. On the other hand, some oral TKIs (TKI) can target multiple pathways. For example, crizotinib can be beneficial for those with an ALK fusion and a ROS1 mutation (NCCN, 2022). Immune checkpoint inhibitors against programmed-death ligand 1 (PD-L1)/PD-1 are beneficial against particular types of lung cancers with a high PD-L1 expression or a high tumor mutational burden, which could vary amongst the different tumors. The rate of expression of PD-L1 in MPLC is relatively small (13.4%). Furthermore, when the genomic profiles of patients with synchronous lung adenocarcinoma and lung squamous cell carcinoma were analyzed from the same patient, distinct tumor microenvironments were observed in the two tumors [13]

While most of the EGFR TKIs develop resistance such as EGFR T790M mutation, analysis of the molecular mechanism of different pathways revealed that downstream pathways such as mitogen-activated kinases (MAPK), MEK/ERK, or PI3K/AKT pathway are reactivated in EGFR T790M mutated cancers and hence develop resistance to TKIs targeted to EGFR. Thus, the MAPK pathway acts as a compensatory mechanism to activate the signal transduction pathway. In NSCLC, mutations such as exon 19 deletion, L858R, and T790M increase kinase activity leading to downstream signaling pathways such as MAPK and other related complex networks of pathways leading to the promotion of tumorigenesis of NSCLC [14]. In addition to this, MAPK and PD-L1 pathways have a cross-talk leading to modulation of T cell activity. Hence immune checkpoint pathways and MAPK and EGFR mutations are related by a complex network of downstream signaling pathways. Furthermore, the MAPK pathway seems to be the primary driver of PD-L1 expression. Thus, mutations in EGFR, ALK, and BRAF induce PD-L1 expression in NSCLC via the MAPK pathway [15].

NGS utilizing a tumor-specific yet broad panel is considered standard of care per the NCCN clinical guidelines for the type of treatment of MPLC. In this regard, Liang et al. [16] have analyzed the different pathways using clinical samples from MPLC and found that apart from EGFR, the MAPK pathway is essential in MPLC and can be targeted to treat MPLC tumors after the genetic biomarker analysis. Although mutations of EGFR, BRAF, KRAS, and RBM10 are found in multifocal pulmonary nodules, EGFR mutations were most commonly found in around 31% of analyzed samples. The most common mutation was EGFR exon 21 L858R. Their analysis found that most clinically diagnosed samples were genetically different, and only a few patients (10 patients) showed genetically similar tumors. Genetically similar tumors were found at different anatomical locations in the same patients. In a cohort of patients, EGFR L858R was shown in nine patients in all nodules. On the other hand, EGFR e19del and e20ins were found in focal specific only. From the pathway analysis study, Liang et al. concluded that the most frequently altered genes in sMPLC samples were MAPK/ERK pathway. The analysis also suggested that patients with MPLC might benefit from EGFR-TKI therapy compared to chemotherapy. Overall, the authors suggest that a large-scale genetic analysis of the data is needed to formulate a therapeutic regime for MPLC and EGFR targeted therapy may have benefits for MPLC compared to immunotherapy. This study is one of the studies that report the large-scale analysis of MPLC samples. Also, epidemiologic variations must be considered when evaluating these mutations. A review of 151 epidemiologic studies regarding EGFR mutations in patients diagnosed with adenocarcinoma NSCLC showed the highest incidence was in Asian-Pacific countries (47%) and the lowest was in Oceanic countries (12%) [17]. Therefore, one may not be able to extrapolate the incidence and common mutations seen in one patient population to another.

Considering the importance of MAPK and other downstream signaling pathways, inhibitors of these compensatory pathways may be more beneficial for treating MPLC and immunomodulating agents. However, the MAPK pathway has an essential role in T cell function, and these downstream signaling pathways are compensatory mechanisms. Therefore, combining immunotherapy with MAPK inhibitors is highly context-dependent. In addition, it depends on the tumor's nature, particularly for MPLC; detailed knowledge about each tumor genetic analysis is needed in the treatment of MPLC.