The investigators postulated that the exploitation of the pro-immunogenic effects of radiotherapy with thymosin might result in abscopal responses among patients with metastatic cancer. The research is designed to evaluate the efficacy and toxicity of patients treated with hypofractionated radiotherapy combined with thymosin alpha 1. An exploratory biomarker analysis in blood and tumor samples is also planned.

Inclusion Criteria:

• Newly diagnosed metastatic lung adenocarcinoma harboring sensitizing EGFR mutations (L858R, exon 19 deletion), and showed stable disease after 3 months TKI, evaluated twice by PET/CT scan, brain MRI, and abdomen ultrasound (≥3 measurable lesions, and these lesions haven't received local therapy)
• Age 18 years or older
• ECOG Performance Status 0-2
• Adequate bone marrow, liver and renal function, as specified below: Absolute Neutrophil Count (ANC) ≥ 1.5 x 109/L; Hemoglobin ≥ 8 g/dL; Platelets ≥ 100 x 109/L; Serum total bilirubin ≤ 1.5 x upper limit of normal (ULN) ; AST and ALT ≤ 2.5 x ULN or ≤ 5 x ULN if liver metastases are present; Serum creatinine ≤ 1.5 x upper limit of normal or creatinine clearance ≥ 60ml/min for patients with creatinine levels above institutional normal
• For women of child-bearing potential, negative pregnancy test within 14 days prior to starting treatment
• Men and women of childbearing age must be willing to use effective contraception while on treatment and for at least 3 months thereafter
• Patients and their family signed the informed consents

Exclusion Criteria:

• Received chemotherapy before TKI therapy
• Brain parenchyma or leptomeningeal disease
• Concurrent malignancies other than non-melanoma skin cancer that require active ongoing treatment
• Any medical co-morbidities that would preclude radiation therapy.