TORONTO - Jack Layton has been diagnosed with another form of cancer and is taking a temporary leave of absence as leader of the federal New Democrats to fight it.

The 61-year-old politician announced he was battling prostate cancer in February 2010, but he says recent tests revealed a new form of cancer and he requires further treatment.

Appearing at a news conference today in Toronto with his wife and fellow politician Olivia Chow, Layton appeared to have lost weight and sounded weak.

Layton said he started to feel pain and stiffness around the end of the most recent session of the House of Commons so after the House rose, he underwent tests at a Toronto hospital.

While those tests showed his battle with prostate cancer is going well, they revealed another form of cancer. Layton didn't elaborate on what type of cancer was discovered.

“On the advice of my doctors, I'm going to focus on treatment and recovery,” he said, his voice sounding raspy. “I will therefore be taking a temporary leave of absence as leader of the New Democratic Party of Canada. I'm going to fight this cancer now so I can be back to fight for families when Parliament resumes.”

Party president Brian Topp with consult the NDP caucus and then convene a meeting of the party's federal council to appoint an interim leader.

Layton says he hopes to return to work by the time Parliament resumes on Sept. 19.

“I wouldn't bet against Jack Layton,” said Topp.

Layton's health had come into question prior to the spring election after he underwent hip surgery in early March, just weeks before the start of the campaign.

But he put most of the concerns to rest as he maintained a rigorous schedule throughout the campaign.

The NDP went on to score more seats than ever and capture official Opposition status for the first time in its 50-year history.