There are many reasons for the occurrence of cancer, mainly including the following aspects. Many men with lung cancer have a long history of smoking. Abnormal hormone levels. Many female breast cancer patients have abnormal estrogen levels. Occupational factors, some patients have long-term occupational exposure to carcinogenic substances such as benzene and asbestos, thus developing tumors. Medical factors, such as long-term exposure to radioactive radiation or radiological examinations, can lead to the occurrence of cancer. V. Patients with reduced immune function may have tumor complications, for example, AIDS patients are prone to Kaposi’s sarcoma, etc. Genetic factors: For example, patients with germline mutation of BRCA gene have higher risk of ovarian cancer and breast cancer in their offspring than the general population.