She is expected to begin treatment with "major surgery" in the next two weeks.
Mickelson was schedules to play in this week's EDS Byron Nelson Classic and defend his championship next week in the Crowne Plaza Invitational.
The Phil and Amy Mickelson Foundation was established in 2004, focusing on youth and family issues. The couple testified before Congress last year, and asked for more money to be spent in schools on math and science.
The couple was married in 1996. They have three children ages 9, 7 and 6.
Mickelson Halts Season as Wife Diagnosed With Cancer [Bloomberg]