"He sent out a confidential email in mid-November to a number of people – personalized, of course," Jane Pauley, a close friend and Brokaw's former Today cohost, tells PEOPLE.
After asking about Pauley's husband Garry Trudeau and their kids, Brokaw made light of the news, writing, "Turns out the Brokaw lucky star has a dimmer switch."
Says Pauley, "This is not good news, but I think we all share his optimism."
In an open note to NBC last week, Brokaw, 74, wrote that despite being diagnosed last August, "I'm still the luckiest guy I know."
Experts say that while some patients require a bone marrow transplant, multiple myeloma can be managed for many years with medication alone.
"He recently gave me an update on his progress, reporting good results," Pauley, 63, says. "Some people retreat from the world when they get news like this … Tom is not one of those people."