Brain Metastasis and Epidermal Growth Factor Receptor Mutations in Croatian Caucasians with Lung Adenocarcinoma

The brain is a common site of metastasis in non-small cell lung cancer (NSCLC). The aim of this study was two-fold: 1) to determine the incidence of brain metastasis (BM) in Caucasian lung adenocarcinoma patients with epidermal growth factor receptor (EGFR) mutations and 2) to evaluate the frequencies and potential relationship of the different EGFR mutations with BM. A retrospective cohort study was conducted at a Croatian tertiary hospital (Clinic for Respiratory Diseases “Jordanovac”) using data collected from medical records. Caucasian patients with primary NSCLC who were tested for EGFR mutation status between January 2014 and October 2015 were included. Of 1040 NSCLC samples tested, 122 (11.7%) patients with lung adenocarcinoma harbored EGFR mutations; six EGFR positive (+) patients (four with BM) had repeat EGFR testing. The majority of EGFR mutants were females (n= 90, 77.6%), non-smokers (including never-smokers and former-smokers; n= 95, 92.2%), diagnosed with advanced disease (stage IIIB/IV) at first presentation (n= 75, 68.8%), and median age at initial diagnosis of primary lung cancer was 65 years (35 - 90). Twenty-three (19.8%) of 116 EGFR+ patients were diagnosed with BM; for six EGFR+ patients, data about BM was missing. Most were 64 years of age or younger (n= 15, 65.2%) at diagnosis of BM (median age: 62 years, 48 - 72). Synchronous BM disease at initial diagnosis of lung cancer was found in 43.5% of EGFR+ patients with BM (n= 10). There were more EGFR+ women with BM (n= 20, 87%) than men. Single exon 19 deletion and exon 21 L858R mutations were the most common subtypes in both EGFR+ patients without BM (n= 44, 47.3% and n= 27, 27.8%, respectively) and with BM (n= 13, 56.5% and n= 5, 21.7%, respectively). One BM patient (4.3%) had a double mutation (exon 19 and 21), while six non-BM patients (6.2%) had simultaneous pairings, most commonly between exon 19 and 20 (n=3, 3.1%). Although exon 18 mutations were seen in six patients without BM (6.2%), none were found in BM+EGFR+ patients. Exon 20 T790M mutation occurred in 17.4% of BM patients (n= 4) versus 15.3% of non-BM patients (n= 15). Rare EGFR double mutations (exon 18 and 20) were found in two non-BM patients (2.2%). Larger long-term prospective studies to explore and confirm these results in BM+EGFR+ patients are warranted. In the era of precision oncology, molecular testing of EGFR mutations may further clarify the pathogenesis of lung cancer-associated BM.