The rapper, whose real name is Curtis Jackson, was planning the tour to support his third solo disc, "Curtis."
His spokeswoman would not comment on Jackson’s remarks that he will retire if his album doesn’t due as well as Kanye West’s third CD, "Graduation."
West topped the U.K. charts on Sunday and he is expected to win the race to No. 1 in the United States later this week, the BBC said.
"If Kanye West sells more records than 50 Cent on Sept. 11, I'll no longer write music," Jackson told the hip-hop Web site, SOHH.com.
"I'll write music and work with my other artists, but I won't put out any more solo albums."
Jackson has also canceled appearances at this week's Mobo Awards and Vodafone Live Music Awards in London, as well as an MTV show in Germany on Friday.