It is often difficult for people to understand why doctors ask patients to undergo chemotherapy before they seem to have recovered from a tumor that has been easily removed by a knife. Whenever chemotherapy is mentioned, many people first associate it with vomiting, hair loss, mental depression, or decreased resistance, and they feel scared of the side effects of chemotherapy. Isn’t chemotherapy a bit difficult for patients who have just recovered from surgery to accept? Why do doctors recommend us to receive chemotherapy soon after tumor removal? Characteristics of malignant tumor Malignant tumor is a systemic disease. Tumor usually grows up in the primary focus, and with the prolongation of tumor growth, local infiltration and distant metastasis will occur, including metastasis through lymphatic vessels, or metastasis through blood circulation to various organs such as liver, lung, brain and bone, thus losing the opportunity of surgical resection. About tumor, the most frequently discussed question is whether tumor can be cut? Are tumors cut? Yes, the current treatment principle of most tumors is: surgical resection as the core comprehensive treatment. For middle and late stage tumors, surgery alone is often difficult to achieve the best results, and chemotherapy is the most important adjuvant treatment. If the tumor is detected early and confined to the local organ (CT or MRI does not reveal local or distant metastasis), the surgeon still has the opportunity to “end” the locally developed tumor through local excision and debulking. However, the problem is that many patients with tumors that have been confirmed to have not developed distant metastases after detailed examination have developed distant metastases again one or two years after surgical resection. Since the primary lesions have been removed, where do the metastases come from? In fact, most of these metastases are developed from microscopic metastases that existed before surgery but could not be detected by clinical examination. These micro-metastases, which exist but cannot be detected by examination, can be called subclinical metastases. Because of the existence of such potential metastases, some patients have “recurrence and metastasis” after a period of time after surgery. In fact, most of the tumors have more or less metastases when they are found. Because of such potential metastases, if neither review nor chemotherapy is given after surgery, the probability of tumor recurrence after surgery is very high. The scary thing about tumor cells is that they are tenacious and only a tiny amount of individual tumor cells can develop into a mass of metastases, which can be described as a star fire that can start a prairie fire. The value of chemotherapy How to deal with these tiny metastatic lesions lurking in the body? In order to destroy these small fraction of “escaped” tumor cells, doctors use chemotherapy to destroy these tiny cancer cells, based on the experience of non-solid tumor treatment. Adjuvant chemotherapy after surgery has been proven to be beneficial in improving the survival rate for most tumors, especially for patients with intermediate to advanced tumors. The more advanced the tumor is found, the higher the probability of metastasis; therefore, physicians usually recommend systemic chemotherapy for patients with advanced stages in order to destroy or control these possible microscopic metastatic lesions. It has been proven that chemotherapy is valuable to prevent tumor recurrence and metastasis after surgery. These chemotherapeutic drugs have the strongest killing effect on the fast-growing tumor cells and also kill the fast-growing cells in our body, such as gastrointestinal cells, hair follicle cells, and hematopoietic cells. Therefore, vomiting, diarrhea, hair loss, anemia, and low resistance are the most common symptoms after chemotherapy with traditional cytotoxic chemotherapy drugs. Most people are impressed by the side effects of chemotherapy through movies and TV shows: vomiting until bile is vomited, hair loss until none is left, and all kinds of unpleasant feelings all over the body. But in reality, this is not the case, and not everyone will have such severe reactions. Not everyone will have such a severe reaction to chemotherapy. In the hospital, you can see many people who do not lose their hair during chemotherapy and walk around during chemotherapy. Traditional chemotherapy drugs can be compared to “explosives that do not distinguish between the enemy and me”, which have a strong killing effect on both normal cells and tumor cells, and can be said to injure a thousand enemies and damage eight hundred. In recent years, molecular targeted drugs have received good effect in tumor treatment, they can target to kill tumor cells while preserving normal cells, which is called “missile that distinguishes between the enemy and me”. For patients with economic conditions, molecular targeted drugs can be used to target tumor cells and reduce the damage of chemotherapy drugs to normal cells. In a word, malignant tumor is a systemic disease. Surgery can destroy the tumor army or nest, but it can do nothing for the scattered and sporadic cancer cells, while the effect of chemotherapy drugs is systemic. Chemotherapy is of great value to prevent tumor recurrence and metastasis after surgery. Whether we can bear the side effects of chemotherapy after surgery we need to weigh the pros and cons and consider them comprehensively.