The former Wales hooker was diagnosed with the illness in October. He underwent surgery and is now awaiting the results of a biopsy.
Rees admits it was been a difficult period but he remains positive and hopes to make his Cardiff Blues comeback during the current campaign.
“It has been a tough six weeks,” Rees told the BBC.
“I have had the operation and am now waiting for the results of the biopsy.
“It has been hard, but I am staying positive and I have finished my first cycle of treatment and start my second next week.
“I am in a positive frame of mind at the moment.”
“Getting back before the end of the season is something I have in the back of my mind.
“But with this sort of diagnosis, I have to take one day at a time and see how it goes but, hopefully, I will be back sooner rather than later.”
Rees won the last of his 58 Wales caps against Ireland in the RBS 6 Nations and was aiming to reclaim a regular spot on the international stage.
He made his Wales debut in 2005 and established himself as the Lions first-choice hooker on the 2009 tour of South Africa.
During the Dove Men Series victory over Argentina, Wales wore jersey’s embroided with special ‘Smiler’ logos in support of the hooker.
