My lung cancer appears inactive but I am still receiving treatment. Do I need to report a change to the VA or wait until they ask?
I'm going to assume you're a Vietnam veteran rated at 100% during a post-treatment period while waiting on a mandatory C & P exam to reevaluate your rating.
No, you do not need to notify VA of anything. In fact, I usually coach vets to learn never to volunteer ANYTHING with VA. Ever. If they ask you any question, you should think of your answer very carefully, in the context of what they may interpret.
For example, you: "I'm an honest guy voluntarily reporting I've improved a lot after my treatments." The VA response: "Dear veteran, thank you for reporting your death. We will proceed to terminate the benefits of the deceased veteran."
OK, sure...that sounds far-fetched but it's an example of what happens on a day to day basis in my world and when you realize things have gone horribly wrong, it's too late. You're in for a nightmare.
If VA asks, answer honestly, briefly and only to the point of answering the specific question. Never volunteer information not specifically asked because VA sees that and judges your motive suspect.
You should be notified around 6 months to a year after your therapy has completed that you'll have an exam coming up. Until then, take care of yourself and don't worry about VA. Good luck sir.