Tom Brokaw -- Diagnosed With Cancer ... But I'm Optimistic

Legendary newsman Tom Brokaw has revealed that he's been diagnosed with bone marrow cancer ... but says he's "optimistic about the future."

74-year-old Brokaw -- who's currently a special correspondent for NBC News -- was diagnosed with multiple myeloma.

According to a study by the National Cancer Institute, the 10-year survival rate for someone of Brokaw's age is 3%.

Still, Brokaw remains positive ... saying, "With the exceptional support of my family, medical team and friends, I am very optimistic about the future and look forward to continuing my life, my work and adventures still to come.”

He adds, "I remain the luckiest guy I know.”

“I am very grateful for the interest in my condition but I also hope everyone understands I wish to keep this a private matter.”