Multiple primary lung cancer (MPLC) is defined as two or more primary lung cancers occurring in the same patient and can be classified as synchronous multiple primary lung cancer (sMPLC) and metachronous multiple primary lung cancer (mMPLC). Due to various clinicopathological characteristics and genetic features, MPLC is increasingly encountered in clinical practice. The distinction between MPLC and intrapulmonary metastasis (IM) is of great importance to clinical treatment and prognosis. However, there are currently no golden diagnostic criteria for MPLC due to tumor heterogeneity. Here, we report the case of a patient with four lung cancers (tumor 1, named T1, in the right middle lobe seven years earlier; tumor 2, named T2, in the left lower lobe; tumor 3 and tumor 4, named T3 and T4, in the left upper lobe) and two tumors (T1 and T2) which shared the mutation in epidermal growth factor receptor (EGFR) L858R/T790M based on targeted multigene sequencing, which indicate that these two tumors might have originated from a common ancestor. However, based on previously published guidelines, these three tumors (T2T4) were diagnosed as mMPLC.