The 64-year-old Hockey Hall of Famer announced his illness Tuesday in an open letter in French on TVA Sports' website.
"For more than six years, through TVA Sports, you have allowed me to enter your living rooms," Bossy wrote. "I've had the privilege of telling you about the game as I understand it, and as I know it. … I wanted to share my experiences with you and you have always been attentive to my words. Thank you.
"Today it is with sadness that I must retire from your screens for a mandatory break. A necessary break during which I will have to receive treatment for lung cancer.
"I can tell you that I intend to fight with the determination and the enthusiasm that you have seen me display on the ice and in my game. That same determination that helped me achieve my dreams and my goals, the one that propelled me to the top of my sport when I was still playing."
Bossy scored 1,126 points (573 goals, 553 assists) in 752 games during his 10 NHL seasons, all with the New York Islanders. The former forward is 22nd in NHL history in goals but his average of 0.76 goals per game is the highest among all players with at least 200 games.
He scored 160 points (85 goals, 75 assists) in 129 Stanley Cup Playoff games, and helped the Islanders win the Cup four straight seasons (1980-83). He was voted the Conn Smythe Trophy as most valuable player of the playoffs in 1982.
Bossy also won the Lady Byng Trophy, awarded annually to the NHL player voted best to combine sportsmanship, gentlemanly conduct and ability, three times (1982-83, 1983-84, 1985-86).
Bossy, who was chosen by the Islanders with the No. 15 pick of the 1977 NHL Draft, was voted the Calder Trophy winner as NHL rookie of the year in 1977-78 after he scored 91 points (53 goals, 38 assists) in 73 games.
It was the first of an NHL-record nine straight 50-goal seasons for Bossy, including five with at least 60.
"He's ultra-dangerous in front of the net," Al Arbour, who coached the Islanders during their championship seasons, said in a profile on Bossy being named one of the 100 Greatest NHL Players in 2017. "His hands are like lightning and he has a great instinct for the puck."
A chronic back injury forced Bossy to retire after the 1986-87 season. He ranks first in goals, second in points, third in assists and seventh in games in Islanders history and was inducted into the Hockey Hall of Fame in 1991.
"Just as the athletes who are on the cusp of delivering the performance of their life, I will need all my strength and all my focus," Bossy said. "Surrounded by my family and friends, I would like to keep this sacred and peaceful privacy, away from cameras and interviews."
