The actress recently underwent a biopsy after a medical test reportedly showed she had a growth on her lung.
A source tells the National Enquirer, "A growth was detected and there were fears that she was going to be diagnosed with lung cancer - just like Paul had been.
"She lives with Paul's passing every hour of every single day, and this scare brought back the vivid nightmares of when he was diagnosed and the long battle he had to endure before he died.
"Joanne was facing the possibility that she would be struck down by the same disease as Paul."
Woodward was relieved when the growth was ruled benign, but the stress of the situation has taken its toll on the 79 year old and pals fear for her health after she turned up to a charity gala in Connecticut looking frail.
The insider adds, "She was pale, and her hair was whiter and thinner."
Newman lost his two-year battle with lung cancer in September 2008, at the age of 83.
Both he and his wife were heavy smokers for much of their lives.