Background: Familial lung cancer is rare. Previous studies have identified random EGFR mutations associated with the inherited lung cancer. Reports also show that TP53 and CDKN2A mutations may predispose individuals to lung cancer, and MUC16 plays important roles in tumorigenesis and metastasis of lung cancer cells through regulating TP53. However, the molecular findings of familial lung cancer are still few. Methods: We have identified an extremely rare family, four siblings diagnosed with lung adenocarcinomas and one with bladder cancer; all lung cancer patients had multiple synchronous nodules. Their father was also lung cancer patient and deceased. We extracted tumor tissue DNA, genomic DNA (gDNA) and circulating cell-free DNA (ctDNA) from the 5 patients and analyzed the DNA samples using a 500-gene next generation sequencing (NGS) panel. Results:TP53 P72R and other 3 CDKN2B-AS1 germline mutations were identified in all the 5 patients. Although the 3 CDKN2B-AS1 mutations are commonly occurred in population according to dbSNP, these observations are consistent with a hypothesis that TP53 P72R and the CDKN2B-AS1 germline mutants may synergize in predisposing the family members to cancer. Interestingly, 3 MUC16 mutations ((rs754254000, rs754856910, and rs746152510) were all identified in the four lung cancer patients, but none were identified in the bladder cancer patient. All of the 3 MUC16 mutants had very low population allele frequency (all below 0.1%,) suggesting that the MUC16 germline mutations may play roles in the familial lung cancer, which is consistent with previous reports demonstrating the involvement of MUC16 in lung cancer cell growth. Moreover, all the four lung cancer patients had somatic mutations of EGFR L858R/exon 19 deletion prior to treatment with EGFR tyrosine kinase inhibitor (TKI), including one patient with L858R and exon 19 deletion in different tumor nodules, which is consistent with molecular characteristics in synchronous primary lung cancer. Conclusions: We have demonstrated in this study that germline MUC16 mutations may predispose the inherited cancer family members to lung adenocarcinomas. This study provides a clue of the cause of familial lung cancer and also warrants further mechanistic study of MUC16 gene in lung cancer.