Everything is governed by the laws of supply and demand in economics.
Lets take a very simplistic viewpoint not even taking into account whole bunch of shit and do some basic maths.
a) Take the net number of total cancer suffers who would be saved worldwide each year, lets call this x.
b) Multiply that number by the sum total of revenue created for them purchasing the drug each year (which would be huge, think how much HIV pills cost) call this y
c) Subtract above number by the number of cancer wards that would become obsolete (who are by in large subsidized by your tax dollars anyway) account for lost revue in jobs in relation to taxpayer money saved for funding such places and those jobs in the first place and figure out net difference.
d) Add in revenue streams created and new jobs created for administrating/distributing/marketing the drugs.
Your creating money and saving money, its a win win.
You are under the assumption that the cure would be in pill form or somehow have to be re administered more than once.
What if it was just a one-time shot (ala vaccination) that was given to everyone for little to no cost? Would it be covered by insurance?
Would insurance companies also suffer extreme losses in revenue?
There are many factors that would potentially be involved, many of which I do not see companies making more money then they are now.
The only upside would be the actual cure of cancer, which does not bring into question the long term ramifications of saving so many lives.