Do you think they already have a cure for cancer but are keeping it from public !
Question: cancer care is big $$$$$$
Answers: cancer care is big $$$$$$
No there isn't. The 'secret cure for cancer' conspiracy theory is a game played by people who have not had or been close to cancer.
I don't know who you mean by 'they':
Drug companies? Well it won't burst anyone's bubble to hear that drug companies are motivated by huge profits rather than people's health; and any drug company discovering a cancer cure would make more money than they could have so far dreamed of making - fame and fortune beyond their wildest dreams.
Scientists, researchers? They and their families develop cancer at the same rate as the rest of the population - they would be dying or watching relatives die rather than revealing this secret cure.
The medical profession? Every medical professional in the whole world would have agreed to keep existence of a cure secret. Every single one. One blabbermouth, one disgruntled researcher or sacked nurse and the whole conspiracy