Haller was diagnosed with the disease a few weeks after joining Dortmund from Ajax Amsterdam in July for €36m and is yet to make his debut for his new side.
Haller is currently undergoing chemotherapy after the tumor was found to be malignant.
"I'm lucky enough to feel well," he told UEFA's official website.
"I am physically able to work, I feel fine from both a mental and a physical point of view, which is of course helpful to fight this disease.
"I have a timescale in mind. If I'm lucky enough not to need surgery, things can go very quickly. Checks are made three weeks after the final phase.
"If I don't need an operation, with the way I train, I'd like to think that I will be in good condition at the end of those three weeks.
"One of the first things I told myself was: 'OK, it's happened to me. I am going to do everything to be good mentally and physically'.
"I was a spoiled child; I never had any worries. This is the first big ordeal I had to face.
"Some people start their lives like that. I was lucky that it came later in my life, so I can’t complain. It's a challenge, a huge challenge, and the fact that you were able to overcome it means that you’re a warrior."
Haller was the third top scorer in the Champions League last season with 11 goals, behind only Robert Lewandowski(13) and Karim Benzema(15).
The former Eintracht Frankfurt and West Ham United frontman struck 47 goals and provided 16 assists in 65 appearances across all competitions for Ajax after joining in January 2021, winning two Eredivisie titles and two Dutch Cups.
