To convert the active sentence "Doctors have made a new medicine to cure cancer" into the passive voice, follow these steps:
1. Identify the object of the active sentence: "a new medicine."
2. Bring the object to the front: "A new medicine."
3. Use the appropriate form of "be" for the tense (present perfect in this case): "has been."
4. Add the past participle of the main verb (make → made): "made."
5. Add the agent (optional in passive) with "by": "by doctors."
Passive: A new medicine has been made to cure cancer by doctors.
(Note: The agent "by doctors" is often omitted if it's not necessary for understanding or is already implied.)