A 60-year-old female was admitted to the department of Hematology/Oncology, The First Hospital of Tsinghua University (Beijing, China) on 5 Nov, 2018 with a history of weakness and anorexia for three days. Her medical history included hypertension, hyperlipidemia and ischemic heart disease for five years, type 2 diabetes mellitus for one year. There was no obvious family history. Physical examination revealed severe pallor without lymphadenopathy or hepatosplenomegaly. Blood test showed white blood cell count 4×109/L,hemoglobin 26 g/L,platelets 76×109/L and reticulocytes 0.11×1012/L. The peripheral blood smear showed 4% myelocytes and metamyelocytes. Laboratory examination revealed elevated lactate dehydrogenase 928 U/L (normal range,120-250U/L),total bilirubin 37.6umol/L (normal range, ≤20umol/L) , indirect bilirubin 19.1umol/L (normal range, ≤18umol/L) , alanine aminotransferase 115.1U/L (normal range, 9-50U/L),aspartate aminotransferase 70.7U/L (normal range, 15-40U/L),alkaline phosphatase 419.9U/L (normal range, 45-125U/L),γ-glutamyl transferase 283.8U/L (normal range, 10-60U/L), creatine kinase 2172.1U/L (normal range, 50-310U/L), triglyceride 2.52mmol/L (normal range, ≤1.7mmol/L) . C-reactive protein 7.73 mg/dl (normal range,0.1-5mg/dl), procalcitonin 0.616ng/mL (normal range,≤0.05ng/mL). Prothrombin time and activated partial thromboplastin time was within the normal range, while fibrinogen degradation product was elevated (16.96 mg/L; normal range,≤5mg/L) , D-Dimer was 2.395mg/L(normal range, ≤0.3mg/L) and fibrinogen (FIB) was 2.39g/L(normal range, 2-4g/L). Human immunodeficiency virus, cytomegalovirus and Epstein-Barr virus were all negative. Also, the immunologic examinations were normal. The tumor marker test demonstrated carcinoembryonic antigen(CEA) 16.34ng/mL(normal range, ≤3.4 ng/mL ), CA125 75.3U/mL(normal range, ≤35 U/mL), CA199 77.69U/mL(normal range, ≤39U/mL), Cyfra 211 12.39ng/mL(normal range, ≤3.3 ng/mL), NSE 311.2ng/mL(normal range, ≤16.3 ng/mL), ProGRP>5000ng/L(normal range, ≤68.3ng/L), ferritin 1432ng/mL (normal range, 30-400 ng/mL) was elevated. Urinalysis showed haematuria and increased urobilinogen. Hemolysis related tests including Coombs’ test, free hemoglobin and paroxysmal nocturnal hemoglobinuria clones were all at the normal level. Subsequent chest computed tomography (CT) scan showed right middle lobe consolidation (Figure 1). Ultrasound examination of the abdomen revealed multiple hypoechoic lesions in the liver. She was transfused with red blood cells intermittently. Despite broad-spectrum antibiotics treatment, she still experienced sustained fever with maximal temperature of 40°C for one week without obvious infective symptoms. Given the high suspicion of HLH,dexamethasone (10mg daily ) was started on the 5th day. Further examination revealed decreased natural killer (NK) cell viability 11.97% (normal range, ≥15.11%) and normal sCD25 1703pg/mL (normal range, ≤6400 pg/mL). Subsequently, flow cytometry analysis suggested 0.04% karyota of suspected epithelial origin non-hematopoietic cells in the bone marrow aspiration. Furthermore, pathological review showed hemophagocytosis and metastatic carcinoma within the bone marrow (Figure 2). Immunohistochemical staining of bone marrow biopsy confirmed metastatic SCLC (Figure 3). The tumor cells were positive for cytokeratin (CK) 7(little +), AE1/AE3(++), CK8/18(++), CK5/6(little +),CD56(+++), Ki-67(80%), CgA(few +), Syn(+++)and TTF-1(+++), but negative for CK20, Napsin A and P63. Up to now, the patient met five of the eight diagnostic criteria of HLH according to the HLH-2004[3]. Therefore,she was diagnosed as SCLC related HLH and quickly underwent the inductive chemotherapy regimen consist of dexamethasone and etoposide (100mg d1) according to the HLH-1994[4 ]on the 7th day (14 Nov, 2018). However, the disease progressed rapidly. Finally, she developed a continuous febrile convulsion and died on the 12th day (16 Nov, 2018).