Democrat John Edwards says his presidential campaign will continue while his wife is treated for a recurrence of cancer. 

The former senator and 2004 vice presidential candidate announced Thursday that his wife's cancer has returned and is not curable.  But he added that both he and his wife Elizabeth are optimistic the disease is treatable.

Elizabeth Edwards discovered she had breast cancer in 2004 during the final stages of her husband's unsuccessful bid as the Democratic vice presidential running mate of Senator John Kerry.  She earlier had been given a clean bill of health after other medical tests.  The cancer has now spread to a rib bone.

Edwards has established himself as a strong third contender among Democrats vying for the 2008 race for the White House.  He trails Senators Hillary Rodham Clinton and Barack Obama in most polls of Democratic voters.

Elizabeth Edwards is a former attorney who has played an active role in her husband's political campaigns.

The couple has been married for nearly 30 years and had four children.  Their oldest son died in a car accident in 1996.