Abstract: Multiple primary malignancies combined with SWI/SNF complex-deficient gastric cancer is a rare clinical entity and poorly documented. Herein we report a case of this disease in an 81-year-old male patient treated in our hospital. Before the established diagnosis of metachronous multiple primary malignancies, the patient received left lower lobectomy for a space-occupying mass in the left lung, which was confirmed by postoperative pathology as early stage lung cancer. SWI/SNF complex-deficiency gastric cancer with metastasis was subsequently detected by gastroscopy, and high-throughput sequencing identified ARID1A and TMB-H gene mutations in the tumor tissues. The patient received chemotherapy combined with immunotherapy but failed to respond to the treatment, and died 13 months later. We conducted a literature review and analyzed the occurrence, pathological and immunohistochemical characteristics, diagnosis, treatment and prognosis of this disease.

Key words: multiple primary malignancies; SWI/SNF complex-deficiency; gastric cancer