A 45-year-old male underwent a left upper lobectomy and postoperative pathology revealed invasive stage IIIA lung adenocarcinoma ( Figure 1 ). Targeted next- generation sequencing (NGS) with a customized panel (Geneseeq Prime panel) designed to target 425 cancer-specific genes was performed, and four somatic mutations and copy number alterations (CNAs) were identified, including EGFR-KDD of exon 18-25 [mutant allele frequency (MAF): 13.5%], EGFR amplification (4.5-fold), TP53 p.Y220C (MAF: 37.0%), and RB1 single copy loss ( Figure 1 ). The tumor mutation burden (TMB) was estimated to be 1.1 mutation/Mb. The patient received pemetrexed and cisplatin as adjuvant chemotherapy. Four months later, he progressed with liver metastasis in left lobe ( Figure 1 ).
Then, the patient was treated with Icotinib and the metastasis shrunk. Unfortunately, the drug resistance was observed only after 4 months, as evidenced by the fact that previously responsive liver lesion progressed. Left hepatic re-biopsy confirmed metastatic adenocarcinoma and target sequencing (Geneseeq Prime panel) detected the same EGFR-KDD (MAF: 4.9%) as well as mutation of TP53 p.Y220C (MAF: 0.5%) ( Figure 1 ). The TMB was calculated as 2.2 mutation/Mb.
Docetaxel and cisplatin were initiated as the second-line therapy. However, the left hepatic metastasis enlarged rapidly after 2 cycles of chemotherapy. The blood carcinoembryonic antigen (CEA) level increased from 9.5 mg/ml (before chemotherapy) to 22.7 mg/ml. Even worse, a right hepatic metastasis appeared soon afterward. Radiofrequency ablation (RFA) of liver was conducted on both of the left and right hepatic metastases, but no reduction in liver lesions was observed, and the CEA level showed a slight increase from 7.3 to 10.3 mg/ml.
Afterward, the patient started taking Osimertinib (80 mg once daily). Encouragingly, both liver lesions showed significant regression ( Figure 1 ). One month after initiation of Osimertinib, the CEA level decreased to 5.4 mg/ml, and remained at normal level for 18 months. Moreover, the progression-free survival (PFS) reached 21 months. However, the CEA level increased to 23.1 mg/ml at the 19th month after the initiation of Osimertinib treatment, and 2 months later, the patient progressed with enlarged mediastinal lymph nodes ( Figure 1 ) with the CEA level of 73.9 mg/ml. Resampling and targeted sequencing (Geneseeq Prime panel) consistently identified EGFR-KDD (MAF: 33.9%), as well as EGFR amplification (6.6-fold), TP53 p.Y220C (MAF: 53.3%), and a new mutation of RELN p.G1774E (MAF: 45.4%) ( Figure 1 ). The estimated TMB increased to 3.4 mutation/Mb. In addition, the assessment of PD-L1 expression using antibody 28-8 (pharm Dx, Dako's Platform) showed tumor proportion score (TPS) of 1%.
On these bases, the fourth-line salvage therapy using Nivolumab was prescribed and the therapeutic efficacy was considerable, as evidenced by the decreased CEA, regressed mediastinal lymph nodes, reduced metastases in both left and right liver ( Figure 1 ). Specifically, the CEA level decreased from 143.6 to 41.8 mg/ml one month later. The PFS reached 7 months and no obvious adverse effects were observed. The quality of life was in good status during the Nivolumab treatment. After that, the patient progressed with enlarged liver metastasis. Unfortunately, the patient was also infected with tuberculosis, and his condition took a sharp turn for the worse due to both tumor progression and tuberculosis. The families gave up further treatment and the patient died 4 months later.