"This morning I shared with my teammates news that I was diagnosed with Chronic Myelogenous Leukemia," Blake said on the team's website.
"It is highly-treatable, and I have begun taking a pill on a daily basis that has proven to be very effective in controlling this cancer. The prognosis, and certainly the expectations of my physician, myself and my family, is that I will live a long, full and normal life. This situation will not impact my ability to live my life as I otherwise would, and will not affect my ability to perform at my highest level for the Toronto Maple Leafs. I'm looking forward to my first season with the Leafs and helping our club compete for the Stanley Cup."
Chronic myelogenous leukemia (CML) is an uncommon type of cancer of the blood cells.
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It's considered chronic leukemia because it usually progresses more slowly than acute leukemia, sometimes over the course of years.
CML is not a solid tumor that can be surgically removed, but the prognosis for people with chronic myelogenous leukemia may be improving because of new medications to treat the condition.
"When you find out that you have something it's definitely shattering to your whole family and so on," Blake said after practice.
"Overall I feel good. I'm still here and my goal this whole season hasn't changed. Obviously you take a step back and you kind of re-evaluate everything but for the most part I feel good. I think to get it off my chest and to move forward is a big weight lifted."
Although a bone marrow transplant may still be an option, many people with chronic myelogenous leukemia are able to manage their condition long term with the use of chemotherapy-like pills.
The team added after Monday's practice that they will be mindful of his condition.
"Jason will be able to continue to play fully with the team and will be monitored closely by both the team's physician and his CML specialist," team doctor Noah Forman said.
It's the second time that Blake's family has been affected by cancer.
In March of 2001, Blake's wife, Sara - eight months pregnant with their first child - was told by doctors that she had thyroid cancer. Blake left the team to be with her, and Lauren Blake was born March 20 after Sara underwent an emergency Caesarean section.
Sara had a portion of her thyroid removed without complications shortly afterwards, and the lump that was removed was determined not to be cancerous.
Toronto signed Jason Blake to a $20 million, five-year contract on July 1.
The four-time 20-goal scorer finished with career highs in goals and points (69) while playing all 82 games with the New York Islanders last season.