A Phase 3 clinical trial that recruited 289 individuals with brain cancer.

The graph shown in Figure 3 summarises the main results of a Phase 3 clinical trial that recruited 289 individuals with brain cancer. The study participants were randomised to one of two treatment groups:

RT: radiotherapy (RT) only

PLT/RT: RT plus three chemotherapy drugs (procarbazine, lomustine and a taxane).

Study participants were followed up at regular intervals for up to seven years, to estimate progression-free survival.

Figure 3 Progression free survival of brain cancer patients treated with radiotherapy alone (RT) or radiotherapy plus PLT chemotherapy (PLT/RT).

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The graph shows progression-free survival (vertical y-axis) from 0 to 100% and years from random assignment (horizontal x-axis) from 0 to 7 years. Two lines show gradual decrease from left to right. The red line (RT, radiotherapy alone) falling more than the blue line (PLT/RT, chemotherapy drugs plus radiotherapy).

Progression free survival of brain cancer patients treated with radiotherapy alone (RT) or radiotherapy plus PLT chemotherapy (PLT/RT).

A. Based on the data presented in Figure 3, which of the two treatment regimens is more effective? Explain how you reached this conclusion.

B. The PLT chemotherapy regimen includes a taxane. What is the mechanism by which taxanes work?

C. Many effective anticancer treatments use combinations of drugs with different mechanism of action. PLT treatment combines taxane with two other drugs, procarbazine and lomustine, which are both alkylating agents.

i. How do chemotherapeutic alkylating agents work?

ii. Why does the use of a combination of drugs with different molecular mechanisms of action (such as PLT) help to counteract the microevolution that can occur in many cancer cells?