You might not need to disclose. If you are still considered employed, and return to work, there is no reason to mention it.

Legally the interviewers can't ask, but they still might, or come to questions about your low flying rate during a period of time, or another way where disclosing might easily explain the problem. Be ready to discuss cancer head-on, in simple-to-understand terms, along with recurrence rates (far lower than chances of freeway accidents). Show perseverance instead of sob story. It takes perseverance to get to a part 135 operator and through training, it takes far more to beat cancer. You've probably learned something about your goals from the experience as well, thus you are focused, determined, and you don't let a bad time get you down.

Your interviewer might have gone through a similar battle which means instant rapport.

Cancer is not the Scarlet "C" it once was.