The difference between first-line, second-line and third-line chemotherapy is that the most useful or effective chemotherapy regimen for a tumor is called first-line. After 4-6 cycles of first-line chemotherapy, if progression occurs, second-line chemotherapy regimen will be used. If the efficacy of second-line chemotherapy is evaluated again after 2 courses of treatment and progression occurs again, the chemotherapy regimen will be switched to third-line chemotherapy. Third-line chemotherapy regimens are often single-agent regimens, or combined with other mechanisms of antitumor drugs, such as chemotherapy plus anti-tumor angiogenesis, or chemotherapy plus targeted drugs, which means that first-line is the preferred choice, second-line is the second choice, and third-line is the alternative.