A Randomized Study to Evaluate the Efficacy of a Reduced Starting Dose of Lazertinib (Leclaza) and Preemtive Magnesium Supplementation to Prevent Lazertinib(Leclaza)-Induced Peripheral Neuropathy

Inclusion Criteria: 1. Pathologically diagnosed pulmonary adenocarcinoma. 2. Patient with a stage not amenable to curative treatment by surgery or radiotherapy and requiring palliative chemotherapy. 3. Patient with no prior treatment history for lung cancer, or who relapsed \>=6 months after curative-intent therapy (concurrent chemoradiotherapy or adjuvant chemotherapy) with no subsequent anticancer treatment - i.e., a candidate for first-line chemotherapy. 4. Patient with a confirmed EGFR mutation of Exon 19 deletion or L858R. 5. Patient able to decide on participation in this study through voluntary decision-making. 6. Age 19 years or more. 7. ECOG PS 0-2. 8. Minimum life expectancy 12 weeks or more. 9. Adequate organ function. Exclusion Criteria: * Subjects with confirmed leptomeningeal/CNS metastasis on brain MRI or cerebrospinal fluid examination. * Subjects with pre-existing peripheral neuropathy. * Subjects who are taking any agent that may affect the development of peripheral neuropathy for reasons other than peripheral neuropathy (magnesium, pregabalin, gabapentin, duloxetine) and refuse to discontinue its use. * Subjects for whom, in the physician's judgment, participation in this study would carry greater harm than benefit (no specific items specified). * Uncontrolled systemic disease, including uncontrolled hypertension, severe heart failure, active bleeding, or active infection. * Pregnant or breastfeeding women. * History of interstitial lung disease (ILD), drug-induced ILD, radiation pneumonitis requiring steroid treatment, or evidence of clinically active ILD. * QTc prolongation based on QTc measured by ECG during the screening period (QTc \>=470 msec). * Subjects with a history of hypersensitivity to Magnes tablet. * Subjects with hereditary disorders of sugar metabolism such as galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption. * Subjects with a history of severe symptomatic renal failure. * Subjects taking a drug expected to have a clinically significant interaction when co-administered with magnesium-containing preparations - such as phosphate preparations, calcium preparations, oral tetracyclines, antacids, or levodopa - for whom discontinuation or substitution of the drug is not possible.