Ashfield issued an open letter Friday to constituents in his riding of Fredericton explaining that recent tests determined he has Hodgkin lymphoma and treatment has begun.
"We were fortunate to have caught this in the very early stages and, with treatment, there is a high rate of successful recovery," Ashfield wrote.
"My treatment has begun and will continue through the summer."
He says he can continue his cabinet duties in the immediate term, but would like to be excused from cabinet at the next shuffle.
"This will allow me to spend more time with my family and focus my energy fully on my riding and serving the people who elected me," he wrote.
Prime Minister Stephen Harper issued a brief comment on Twitter, saying he and his wife Laureen are saddened by Ashfield's news and wish him well in his recovery.
A spokesman for Harper's office said they wouldn't issue any further statement or speculate on the timing of a cabinet shuffle.
New Brunswick Premier David Alward issued a statement, saying he spoke with Ashfield on Thursday evening.
"Our thoughts and prayers are with Keith and his family as he takes on his most important fight to date," Alward wrote.
Ashfield suffered a heart attack last year and underwent bypass surgery.
A spokeswoman for the minister said Ashfield was not available for interviews.
The 61-year-old politician was first elected to the New Brunswick legislature in 1999 and was elected federally in 2008.
He also serves as minister for the Atlantic Gateway and regional minister for New Brunswick.
The statement says Ashfield plans to continue to serve as a member of Parliament.
About 900 Canadians are diagnosed with Hodgkin lymphoma each year.
Note to readers: This is a corrected story. A previous version said Keith Ashfield was first elected to the New Brunswick legislature in 1991.
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