“This is a very difficult message for me to write,” said Brooks.
“I have been diagnosed with Stage 2 Hodgkin lymphoma and will begin a course of treatment next week.
“Although this has come as a shock to myself and my family, the prognosis is a positive one and I am confident that I will make a full recovery and be back playing as soon as possible.”
Hodgkin lymphoma is a cancer of the lymphatic system, an important part of the immune system.
“I’d like to show my appreciation to the doctors, nurses, consultants and staff who have been treating me for their professionalism, warmth and understanding during this period,” Brooks said.
“I want to thank everyone at the Football Association of Wales because without the swift attention of their medical team we may not have detected the illness.
“I’d also like to say thank you to AFC Bournemouth for all of their support and assistance this past week.”
Brooks has played nine times for Championship side Bournemouth this season, scoring three goals, but his football career will now be on hold as he begins treatment.
“Although I appreciate that there will be media attention and interest, I would like to ask that my privacy is respected in the coming months and I will share updates on my progress when I am able to do so,” Brooks added.
“In the meantime, thank you to everyone for their messages of support – it means so much and will continue to do so in the months ahead.
“I look forward to seeing you all again and playing the sport I love very soon.”
Both Wales and Bournemouth have offered their support and best wishes to Brooks during his treatment.
Brooks, who made three appearances for Wales at Euro 2020, last played in the Cherries’ goalless draw against Peterborough on 29 September, when he came off after 69 minutes.
Wales announced on 6 October that he had withdrawn from their latest squad through illness.