Risk Factors of Brain Metastasis in Patients with EGFR-Mutated Advanced Non-Small Cell Lung Cancer


 Purpose NSCLC patients with EGFR mutation was associated with higher incidence of developing brain metastasis (BM). BM is associated with high mortality. Reducing risk of BM becomes increasingly significant for achieving prolonged survival. The aim of the study was to explore the possible risk factors of developing BM during EGFR-TKIs treatment, and to identify the potential candidates for prophylactic cranial irradiation (PCI) or the first-line osimertinib treatment.Methods A total of 157 consecutive EGFR-mutated advanced NSCLC patients without BM at initial diagnosis in our institute between 2014 and 2018 were included. Comparisons of OS were performed based on BM status. The cumulative incidence of secondary BM was calculated by the Kaplan-Meier method, and the independent risk factors of secondary BM were investigated by multivariate analysis.Results Patients with secondary BM had worse survival (mOS: 28.6 months) than patients not-developing BM (mOS: 44.8 months). Moreover, the multivariate analysis indicated that age ≤ 49 years (P=0.035), number of extracranial metastases (P=0.013), and malignant pleural effusion (P =0.002) were independent risk factors of secondary BM. Furthermore, the 1-year actuarial risk of developing secondary BM in patients with no risk factor (n =101), 1 risk factor (n =46), and 2 risk factors (n =10) were 7.01%, 14.61%, and 43.75%, respectively (P<0.001).Conclusions Patients developing secondary BM during EGFR-TKIs treatment have worse outcomes. Our results suggested that EGFR-mutated advanced NSCLC patients with ≥ 1 risk factors were candidates for PCI or the first-line osimertinib treatment.


Introduction
Lung cancer is the leading cause of cancer death all over the world [1]. 80-85% of patients are diagnosed as non-small cell lung cancer (NSCLC) [2]. Despite the presence of the blood-brain barrier (BBB), brain is still a frequent site of NSCLC metastasis. 10% of NSCLC patients present brain metastasis (BM) at their initial diagnosis, and 40-50% of patients develop secondary BM during the course of the disease [3]. The median survival in patients who experience BM without treatment is less than 1 month, and the median survival after whole brain radiation therapy (WBRT) was only 3-6 months [4]. BM is associated with high morbidity, poor prognosis, neurocognitive and life quality deficits [5]. Therefore, reducing risk of BM becomes increasingly significant for achieving prolonged survival.
Epidermal growth factor receptor (EGFR) mutations are observed in approximately 10-15% of the Caucasian population [6] and more than 50% of the Asian population [7] with non-squamous NSCLC. It was reported that NSCLC patients with EGFR mutation was associated with higher incidence of developing BM [8][9][10]. In addition, EGFR-tyrosine kinase inhibitors (TKIs) largely improved the survival of EGFR-mutated advanced NSCLC patients [11][12][13], whereas patients with longer survival exposed to higher risk of BM [8]. Although EGFR-TKIs was reported to pass through BBB and reduce BM in EGFRmutated NSCLC patients [14,15], there remain some patients developing secondary BM during the course of EGFR-TKIs therapy. Lee et al found that 26% of the patients developed central nervous system (CNS) failure and 13% experienced isolated CNS failure among 166 patients with a clinical benefit to first-generation EGFR-TKIs (gefitinib or erlotinib) treatment [16]. Moreover, EGFR-mutated NSCLC patients with BM had a worse median OS of 25.1 months than the patients without BM (30.2 months) [17]. These results suggested that it was necessary for EGFR-mutated advanced NSCLC patients to reduce risk of developing BM.
How to reduce risk of developing BM for EGFR-mutated advanced NSCLC patients. Firstly, prophylactic cranial irradiation (PCI) is a technique that delivers radiation therapy (RT) to the whole brain to prevent BM occurrence. It was reported to significantly reduce risk of BM and improve overall survival (OS) in patients with limited-stage small cell lung cancer (SCLC) [18]. In addition, osimertinib is an oral, irreversible third-generation EGFR-TKIs with higher penetration in CNS [19][20][21]. FLAURA study showed the frequency of events of CNS progression was lower in the osimertinib group than in the standard EGFR-TKIs group [21]. However, the results of RTOG-0214 on the effects of PCI in localized NSCLC indicated that PCI reduced BM incidence, whereas failed to improve overall OS [22] and leaded to decline in immediate and delayed recall [23]. But the 10-years update of RTOG-0214 indicated that patients treated non-operatively have an improved OS (P = 0.026, HR = 1.42, 95% CI: 1.04-1.94) and DFS (P = 0.014) by subgroup analyses, suggesting that PCI might not benefit all patients. For osimertinib, only patients with BM were required to have regular brain scans in FLAURA study, some cases of asymptomatic progression may not have been detected [13]. Moreover, considering the cost of osimertinib, the first-line osimertinib treatment for EGFR-mutated advanced NSCLC patients still not widely available in most developing countries. These findings prompted us to identify population subsets with higher risk of BM. These patients are candidates for PCI or the first-line osimertinib treatment. Previous studies identified several risk factors of BM in NSCLC, including younger age [24][25][26], non-squamous cell carcinoma [24], high serum CEA level [27], and disease stages [25,28].
However, they are still controversial and not specific for EGFR-mutated advanced NSCLC patients developing BM during the course of EGFR-TKIs therapy.  Table 1 Treatment and Follow up Among the 157 patients without BM at initial diagnosis, 24 patients received chemotherapy as their first-line therapy, and the other 133 patients received EGFR-TKIs treatment initially. EGFR-TKIs (gefitinib, erlotinib, or icotinib) were continuously administered until progression of disease (PD) or intolerable side effects. Treatment beyond PD was allowed upon the judgement of continuously clinical benefit by the oncologists.
Follow-up examinations were performed every 2 months, including thoracic and abdominal CT scan, brain MRI scan. Progression-free survival (PFS) was defined as the time from EGFR-TKIs treatment to PD (including local, regional, or distant progression) or death from any cause. OS was defined as the time from EGFR-TKIs treatment to death from any cause. Brain-metastasis-free survival (BMFS) was defined as the time from EGFR-TKIs treatment to BM occurrence. Treatment responses were evaluated by the response evaluation criteria in solid tumors as complete response (CR), partial response (PR), stable (SD), and progression (PD).

Statistics
All statistical analyses were conducted using Statistical Package for Social Scientists (SPSS/Windows, Version 22.0, SPSS Inc., Chicago, USA). Descriptive statistics were used for categorical variables (frequency and percentage) and continuous variables (median and range). The cumulative incidence of BM and survival were calculated by the Kaplan-Meier method with 95% confidence intervals (CIs).
Univariable and multivariable Cox regression analyses were performed to explore the risk factors of secondary BM. The multivariable Cox regression analysis simultaneously included factors that had shown associations (P < 0.100) in the univariable Cox regression analyses, and variables based on their clinical significance according to previously literature reports. The optimal cut-off values of continuous valuables were calculated by X-tile software [29]. All tests were two-sided and P < 0.05 were considered statistically significant.
The overall response rates were partial for 76.4%, stable for 23.0%, and progressive for 0.6% of EGFR-TKIs treatment at the first follow-up examination.
Overall survival of patients grouped by BM status The factors showing associations (P < 0.100) in the univariable Cox regression analyses, as well as other factors that were reported to be associated with BM in previous studies [27,31] were further examined by multivariable Cox regression analysis. Results of multivariate analysis indicated that age ≤ 49 years (P = 0.035), numbers of extracranial metastases (P = 0.013), and documented malignant pleural effusion (P = 0.002) were independent high-risk factors of developing secondary BM. Whereas the first-line treatment regimens and types of EGFR mutations were not associated with secondary BM in multivariate Cox regression analysis. Furthermore, the 1-year actuarial risk of developing secondary BM in patients with no risk factor (n = 101), 1 risk factor (n = 46), and 2 risk factors (n = 10) were 7.01%, 14.61%, and 43.75%, respectively (P < 0.001, Fig. 3). Obviously, patients with more risk factors had a higher risk of developing secondary BM. Our studies suggested that the patients with ≥ 1 risk factors were more likely to benefit from PCI or were candidates for the first-line osimertinib treatment.

Discussion
During the past two decades, the advances of EGFR-TKIs revolutionarily improved the prognosis of EGFR-mutated advanced NSCLC patients. The WJTOG3405 trial reported that the median OS of patients with EGFR-mutated advanced NSCLC was up to 30.2 months [32], which is non-inferior to the outcomes of patients with stage III disease. Our results of 157 EGFR-mutated advanced NSCLC patients without BM at initial diagnosis showed a median OS of 37.5 months and a median PFS of 13.6 months (Fig.1). Although EGFR-TKIs was reported to be more effective than chemotherapy for BM in EGFR-mutated NSCLC patients [14,15], patients with longer survival exposed to higher risk of BM [8], and patients with EGFR mutation was associated with higher incidence of developing BM [8][9][10]. In our study, 30 patients (30/157, 19.1%) developed secondary BM during first-generation EGFR-TKIs treatment, and 1-, 2-and 3-year risks of developing BM were 11.6%, 22.6% and 29.4% respectively ( Fig.1). Therefore, the first-generation EGFR-TKIs therapy resulted in decreased risk of non-BM but had limited impact on BM.
It was well known that BM is a common reason leading to treatment failure associated with poor prognosis [33]. In our study, compared with patients without BM, patients developing secondary BM during the course of EGFR-TKIs treatment were at higher risk on OS (HR = 1.86, 95%CI:1.07-3.26).
Our findings confirmed that patients with secondary BM had worse outcomes (Fig.2) on the condition that there was no difference on clinical and treatment characteristics between the two groups grouped by BM status (Table 1). Therefore, reducing risk of BM in EGFR-mutated advanced NSCLC patients becomes increasingly significant for achieving prolonged survival.
The use of PCI or first-line osimertinib treatment could reduce risk of developing secondary BM for EGFR-mutated advanced NSCLC patients. However, existing evidences suggest that PCI might just suitable for patients with a high risk of developing BM, and the high cost of osimertinib leaded to the first-line osimertinib treatment limited in most developing countries. Therefore, it is important to identify population subsets with higher risk of BM as candidates for PCI or the first-line osimertinib treatment. But there is a lack of data for EGFR-mutated advanced NSCLC in literature.
In the present study, multivariate analysis indicated that age ≤ 49 years was correlated with higher risk of secondary BM (Table. 2). Despite the difference of age cut-off, our results were consistent with previous studies [25,34]. The underlying mechanism is still to be investigated. It was partly interpreted that young people may have better performance status, which are associated with longer survival. Moreover, several studies have shown that BM is associated with the angiogenic microenvironment, and the cerebrovascular microenvironment factors of young patients may be better than those of older patients [35]. Further investigations are required to identify the specific reasons that younger patients are more likely to develop BM.
The numbers of extracranial metastases and malignant pleural effusion were also independent risk factors of secondary BM (Table. 2). The underlying mechanism was also unclear. It may be interpreted that both pleural effusion and BM is associated with the angiogenic microenvironment [35]. In addition, the numbers of extracranial metastases are reflection of tumor burden, which was positive correlated with the development of BM.
Furthermore, our results confirmed that the predictive value of gender and KPS score for secondary BM may remain controversial [36]. Previous studies reported that elevated CEA [27,31,36], NSE [24], and CA125 [24] were independent risk factors of BM. However, there is no correlation between tumor markers levels before treatment (including CEA, NSE, and CA125) and the secondary BM in our study.
And the first-line treatment regimen was also not associated with secondary BM in our multivariate Cox analysis. Koo et al [37] reported that EGFR-TKIs were effective for EGFR-mutated NSCLC, regardless of treatment timing, which is consistent with our results. In addition, EGFR exon 19 or 21 mutations are now well recognized as different prognostic markers for NSCLC. A recent retrospective study [31] showed that point mutations in exon 21 were independent risk factors of BM. However, our results failed to show a statistical difference in the association between types of EGFR mutations and secondary BM.
Furthermore, the 1-year actuarial risk of developing secondary BM in patients with no risk factor (n = 101), 1 risk factor (n = 46), and 2 risk factors (n = 10) were 7.01%, 14.61%, and 43.75%, respectively (P < 0.001, Fig. 3). Obviously, patients with more risk factors had a higher risk of developing secondary BM. Our studies suggested that the patients with ≥ 1 risk factors were more likely to benefit from PCI or were candidates for the first-line osimertinib treatment. Certainly, there are several limitations in our study, this was a retrospective study in a single institution, which inevitably resulted in a selection bias. More finely devised prospective and random study is needed to confirm our results, and the mechanisms of the correlation between these risk factors and secondary BM is to be further explored.
At last, the findings of this study were as follows. First, our studies confirmed EGFR-mutated advanced NSCLC patients with secondary BM had worse outcomes. Second, the multivariate Cox analysis indicated that younger age (≤ 49 years), more extracranial metastases, and malignant pleural effusion were independent risk factors of secondary BM. Third, the patients with more risk factors are more likely to benefit from PCI or the first-line osimertinib treatment.
List Of Abbreviations BM, brain metastasis; PCI, prophylactic cranial irradiation; BBB, blood-brain barrier; CI, confidence interval; EGFR, epidermal growth factor receptor; NSCLC, non-small cell lung cancer; SCLC, small cell lung cancer; WBRT, whole brain radiation therapy; SRS, stereotactic radiosurgery; CNS, central nervous system; NGS, Next Generation Sequencing; NSE, neuron-specific enolase; DFS, disease free survival; OS, overall survival; PD, progression of disease; PFS, progression-free survival; BMFS, Brainmetastasis-free survival; CR, complete response; PR, partial response; SD, stable; TKI, tyrosine kinase inhibitor; VEGF, vascular endothelial growth factor. Declarations agreement to be accountable for all aspects of the work: All authors.   Figure 2 Kaplan-Meier plot of OS in patients with EGFR-mutated advanced NSCLC grouped on BM status. OS, overall survival; NSCLC, non-small cell lung cancer; BM, brain-metastases; CI, confidence interval.

Figure 3
Comparison of the actuarial risk of developing secondary BM among patients with different numbers of risk factors.