The patient, male, 78 years old, was admitted to the hospital with “coughing and sputum for more than 10 days”. The patient presented with cough and sputum more than 10 days ago, with a small to moderate amount of yellow mucus sputum, and went to the local municipal Chinese medicine hospital for consultation. /L”, chest CT showed “large lesion in the lower lobe of the left lung with uneven internal density and a small to moderate amount of pleural effusion on the left side”; diagnosis of “left lung abscess and pleural effusion on the left side”, the patient was hospitalized with anti-infection treatment. Body temperature 38.0～38.5℃, coughing sputum did not improve significantly. Physical examination: body temperature 37.5℃, blood pressure 105/65mmHg; clear, mental well; no obvious enlarged lymph nodes on the superficial surface; trachea in the middle; no deformity of the chest wall, low respiratory sounds in the left lower lung, can hear a little wet mu 115 times/min, rhythmical, no pathological murmur; abdomen flat and soft, no pressure pain rebound pain, liver and spleen not reached under the ribs, mobile turbid sound negative; no edema in both lower limbs, no pestle finger (toe) in the limbs. No obvious pestle-like fingers (toes), no redness, swelling and pressure pain in bilateral knee joints. Laboratory tests: biochemistry: albumin 23.7g/L, sodium 151mmol/L, potassium 2.91mmol/L, no significant abnormalities in cardiac enzymes, troponin and calcitoninogen; lung cancer antigen non-specific esterase 28.1μg/L (0~16.6), cytokeratin 19 fragment 15.5μg/L (0~3.5); squamous carcinoma-associated antigen 0.6μg/L (0~1.5) （Bone marrow aspiration showed that the granulocytic lineage was actively proliferating, mainly in the middle-aged stage and below, and the first consideration was infected bone marrow; external iron +++. After admission, the blood count was checked several times. The white blood cells were progressively increased, the neutrophil ratio remained above 90%, and the C-reactive protein fluctuated from 42 to 110 mg/L. Chest CT showed a large high-density shadow in the left middle and lower lung with uneven internal density, and multiple lymph nodes in the mediastinum were enlarged with mild to moderate enhancement (see Figure 1, 2). Fibronectomy showed a left lower lobe bronchial stenosis with normal luminal mucosa. Lung histopathology revealed sarcomatoid carcinoma after CT-guided lung puncture. Due to the patient’s advanced age and poor physical condition, radiotherapy and chemotherapy were abandoned, and the patient died 2 weeks after the diagnosis was clear. Discussion The patient had a short course of disease with progressive increase in white blood cells within a short period of time, but the inflammatory manifestations were not obvious, and only persistent low to moderate fever was manifested, and the lung mass was progressively enlarged, and finally the sarcoma-like carcinoma was clearly identified. So why do lung cancer patients have such high white blood cells? First, let’s understand what diseases usually produce leukocytosis? The most common one is infection, where the body’s leukocytes (predominantly neutrophils) are released from the bone marrow into the blood at an accelerated rate, cells are transferred from the marginal pool to the circulating pool in the circulation, and cells are reduced from the blood into the tissues. However, these conditions are temporary in nature and are mostly mild. Persistent moderate to significant neutrophilia is due to increased production of hematopoietic stimulation of the bone marrow, which may be caused by continuous application of hormones or exogenous colony-stimulating factors, although the patient did not have long-term use of these drugs. Therefore, it can be inferred that this patient is suffering from a hematologic complication of lung cancer, leukocyte-like reaction. Several studies have confirmed that lung cancer cells, especially the more malignant sarcomatoid carcinomas, secrete large amounts of various colony-stimulating factors, such as G-CSF and GM-CSF (granulocyte-monocyte-colony-stimulating factor). For example, Adachi found high expression of several CSFs by mRNA extraction from pathological tissue specimens of leukocytosis-prone lung cancer patients. Is leukocytosis common in patients with lung cancer? The answer is yes, what does GM-CSF mean for lung cancer patients?In 2001 from Kasuga observed for 7 years reported that 227 lung cancer had 14.5% with tumor-associated leukocytosis [2]. In another report, increased G-CSF or GM-CSF was detected in 47% of lung cancer patients with leukocytosis [3]. For the relationship of lung cancer stage, the highest expression was found in stage III lung cancer, but GM-CSF concentration was lower in stage IV lung cancer than in stage III lung cancer [3]. In addition, the prognosis of lung cancer combined with leukocytosis tends to be more off, and one study showed that patients with preoperative leukocytosis in lung cancer had a five-year survival rate of only 28% compared to 69% for patients with normal leukocyte counts [4]. Another study showed that the median survival of lung cancer patients with combined leukocyte-like reactions was only 4.6 months compared to 20.8 months in patients without leukocyte-like reactions [2]. The topic of whether GM-CSF secretion by tumor cells promotes the growth of lung cancer remains controversial. It has been suggested that G-CSF receptors are expressed on tumor cells, and stimulation by G-CSF promotes the growth of tumor cells. But on the other hand, the antibody-dependent cytotoxic effect of leukocytes that increase and migrate to tumor tissues after G-CSF stimulation may also have an anti-tumor effect. How to treat leukocytosis associated with lung cancer? For example, a case of leukocytosis with eosinophilia has been reported in which a lung mass was shown on CT and the leukocyte count rapidly returned to normal after surgical removal.