The present study selected two patients with lung cancer and epidermal growth factor receptor ( EGFR ) mutations who were treated with a programmed cell death protein 1 (PD-1) antibody and an immunomodulatory arabinomannan extracted from Mycobacterium tuberculosis . In the first case, a 67-year-old female was diagnosed with lung adenocarcinoma with an EGFR mutation (exon 19 deletion) and Stage IVB disease. Initial treatment with an EGFR mutation-targeted tyrosine kinase inhibitor (TKI), erlotinib, demonstrated a partial response. After disease progression this was followed by carboplatin and pemetrexed with bevacizumab, and re-challenged by erlotinib plus bevacizumab; however, the tumor eventually progressed. Subsequently, the patient was treated with immunomodulatory arabinomannan for 3 months. Immediately after, she was treated with nivolumab and showed a partial response. In the second case, a 57-year-old male with a history of smoking was diagnosed with stage IVB pulmonary adenocarcinoma with an EGFR mutation (exon 19 deletion). He was treated with afatinib, followed by osimertinib when a T790M mutation was identified later. After disease progressed with TKIs, cisplatin plus pemetrexed and re-challenge with erlotinib plus bevacizumab were administered subsequently. Nivolumab was administered for recurrent disease. Although he experienced tumor remission, regrowth of the tumors was observed. Under continuing nivolumab, he was treated by palliative irradiation treatments to the right pelvic bone metastasis and left adrenal metastasis with immunomodulatory arabinomannan. A chest computed tomography scan showed a reduction in the sizes of the primary site and pulmonary metastases, with a decreasing trend of carcinoma embryonic antigen. Overall, these cases may indicate that the immune adjuvant actions of immunomodulatory arabinomannan extracted from Mycobacterium tuberculosis improves the effect of PD-1 antibody treatments.