The 67-year-old told Good Morning America he was "doing really good" after having surgery in July.
Knowles said he went to his doctor and got a mammogram after seeing recurring dots of blood on his shirt and sheets.
The music executive and public speaker admitted he had thought "why me?" on learning he had the condition.
"Of all the things I could get, why would I get this?" he told GMA interviewer Michael Strahan.
Male breast cancer is rare and usually occurs in men over 60.