Being a cancer survivor of 5 years, I agree with bigphez that is is something that the medical community does not focus on enough. I went through at least a year of severe depression AFTER my initial statement of remission. I did not realize it was depression until many years down the road.
To future survivors be careful and realize that you are not invincible just because you survived cancer, guard your emotions, and realize that not everyone will understand where you have been and what kind of journey you had.
But also don't forget to rejoice in it also.
and to answer your question no, I did not seek treatment until many years down the road to talk about my experience, I do wish I would have though right away, maybe I would have understood the reason I felt the way I did.