We report the case of a 61-year-old man with squamous cell carcinoma of the left lung and mediastinal lymph node metastases who received nivolumab and experienced a better antitumor effect than expected but died soon afterward. A clinical analysis showed that the grades of the treatment-related events did not cause death. The immunological impact of this treatment on his body, especially at his age and with concurrent infection, possibly augmented by the blockade of the PD-1/PD-L1 signaling pathway, is proposed to be one of the key factors for his death. Consequently, we suggest that the cellular immune status and the clinical characteristics of patients, especially the symptoms like concurrent infection, should be considered in the design of clinical protocol of such a kind of therapy.