The former Team Canada star, who is battling chronic lymphocytic leukemia, says his body responded well to recent treatment in the United States.
He credits his wife, Eleanor, for getting him into a clinic trial.
"I got into that study back in September. I was down 18 pounds. I had a tumour in my stomach the size of a grapefruit, and I was not in very good shape," Henderson said Monday.
"After seven months of this clinical trial that she was instrumental in getting me into, the tumour in my stomach is now the size of the end of my finger, and I've put 16 of those pounds back on and I am doing well."
The 69-year-old native of Kincardine, Ont., is best known for scoring the game-winning goal in Game 8 of the 1972 Summit Series against the Soviet Union.
On Monday, he was among three hockey greats awarded the Order of Hockey in Canada. Six-time Stanley Cup winner and Hall of Famer Mark Messier and coaching legend Dave King also received the Hockey Canada honour at a televised ceremony on Parliament Hill.
Henderson, who played in Detroit, Toronto and Atlanta, says there was no greater honour than playing for his country.
"I'm a very, very proud Canadian, and having the privilege to represent my country on the international level was the highlight of my 18-year career," he said.
"And today is simply the icing on the cake."