An 86-year-old male patient presented to Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, because of the increase of CA-199 level to 282.9 U/mL in regular physical examination, without nausea, vomiting, acid reflux, belching, or other symptoms with an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 1. First, abdominal contrast-enhanced CT was performed, and showed that the gastric wall of cardia was thickened with abnormal enhancement in arterial phase, the outer margin of gastric wall was rough, and multiple nodules were scattered in hepatogastric ligament, retroperitoneum, peritoneum, omentum majus and mesangium. The malignant tumor infiltrated the entire layer of gastric cardia, and multiple round lymph node were highly suspicious for metastasis in the abdominal cavity. Second, the upper GI endoscopy subsequently identified proliferative ulcers in the region of the cardia, and signet ring cell carcinoma was confirmed by pathology. PET/CT was also demonstrating obvious cardia thickening with significant FDG uptake (SUvmax 14.3), as well as increased metabolic activities in the enlarged abdominal lymph nodes (SUvmax 4.9 to 6.8), and nodular thickening of the right retroperitoneum (SUvmax 3.8). Immunohistochemical stainings of the gastric tissue demonstrated positive expressions of MLH1, PMS2, MSH2, and MSH6, PD-L1 combined positive score (CPS) of 20, Ki-67 expression level of 90%, and negative HER-2 expression (Figure 1). He was diagnosed with metastatic gastric cancer with multiple abdominal cavity lymph node and peritoneal metastases (HER2 negative, pMMR, and PD-L1 CPS 20). Chemotherapy was recommended as the first-line treatment, but the patient and his family refused due to his old age and frailty. Given his high PD-L1 CPS and the significant overall survival (OS) improvement in patients with CPS >= 10 treated with pembrolizumab compared to those with chemotherapy in the KEYNOTE-062 trail, he was recommended and administered with 100 mg pembrolizumab as the first-line chemotherapy every 2 weeks for 5 cycles (Figure 2). Ten days after the last dose, the patient presented for icteric sclera and skin and generalized pruritus. He was administrated with the ursodeoxycholic acid (250 mg, bid) in other hospitals for 1 week before admission to our hospital, but the above symptoms did not improve. After addimission, the patient remained hemodynamically stable and the abdominal exam findings were benign. On serum biochemical testing, a marked increase in total and direct bilirubin and slight increase in gamma-glutamyl transferase were identified, the level of alkaline phosphatase (ALP; range, 30-120 IU/L) also increased, but alanine aminotransferase (ALT; range, <50 IU/L) and aspartate aminotransferase (AST; range <50 IU/L) were within normal limits (Table 1). We assessed the tumor status, and a partial response (PR) was assigned according to RECIST criteria. Neither magnetic resonance cholangiopancreatography (MRCP) nor abdominal computed tomography (CT) showed significant biliary obstruction or bile duct dilatation (Figure 3). Tumor progression, and biliary inflammation and obstruction were ruled out. We suggested liver biopsy for differential diagnosis, but the patient and his family refused due to his old age and poor physical condition on admission. Given the patient's PD-1 treatment history, we therefore diagnosed him with immune-related cholestatic hepatitis was diagnosed, and ICI treatments were suspended. The patient received pulse therapy with 80 mg methylprednisolone. Simultaneously, ursodesossicolic acid was administrated to this patient daily. Icterus resolved after 3 days, and the pruritus significantly improved. Total bilirubin decreased from 171.4 to 139.3 mumol/L and direct bilirubin decreased from 114.3 to 88.4 mumol/L after 3-day high-dose steroids treatment. Therefore, oral dexamethasone replaced the methylprednisolone with a tapered dose (dexamethasone 7.5 mg for 4 days, 6 mg for 4 days, and 3 mg for 4 days). Total and direct bilirubins continued to decreasedecreasing, and he was discharged from hospital on day 36 (see Table 1). One month later, the patient developed asthma with a low-grade fever that increased slightly (37.8-38.5 C) in the hospital. Oxygen saturation was low at 78-90%, and a decreased white cell count (1.56 x 109/L; range [4-10 x 109/L]), high levels of C-reactive protein (72 mg/L; range, <10 mg/L), and procalcitonin (0.1 ng/ml; range, <0.5 ng/mL) were found on blood tests. The 1, 3-beta-D-glucan detection (G test) and galactomannan antigen detection (GM test) were performed using blood samples, while bacterial and fungal cultures were performed on sputum and blood. In addition, SARS-CoV-2 nucleic acid test through throat swab specimens and tuberculosis -related sputum and blood tests were also performed. All tests were negative and the antibiotic, Cefoperazone Sodium and Sulbactam Sodium(sulperazone), was administered with granulocyte-colony stimulating factor to promote leucocyte production; however, no significant symptomatic improvement was seen. Another chest CT showed interstitial changes, and interstitial pneumonia was considered probable (Figure 4). He was diagnosed with type 1 respiratory failure based on the report of arterial blood gas examination and treated with high-flow nasal oxygen. A multi-disciplinary consultation was completed, and since the patient had received a PD-1 inhibitor, a consensus considered immune-related pneumonia to be likely. However, because the patient was elderly and treated with glucocorticoids for a considerable time, opportunistic infections could not be excluded. Therefore, the patient was given pulse therapy with 80 mg methylprednisolone and levofloxacin, meropenem, and sulfamethoxazole/trimethoprim. No significant improvements were seen after 3 days, and the patient was transferred to ICU for high-flow oxygen and intravenous immunoglobulin (25 g/day) therapy. An antifungal drug, caspofungin(coses), was also added. Symptoms improved 6 days later, and resolution of the interstitial lung changes was seen on CT (Figure 4). The patient was discharged, and antibiotics were discontinued. At a 1 month recheck, the patient was in good general health with an ECOG PS of 1, and bilirubin levels were within normal limits (Table 1). Enhanced CT of the abdominopelvic cavity showed that PR was maintained (Figure 2) with progression-free survival (PFS) of 7 months.