Chandini Portteus was brought in to help bolster the foundation as it struggles to recover from declines in revenues and donations after founder Lance Armstrong's performance-enhancing drug use scandal.
According to publicly released financial records, Livestrong had a 29 percent drop in revenue in 2014, the second straight year of sharp declines, before Portteus arrived.
In a statement today to The Associated Press, Portteus and Livestrong board chair Candice Aaron say Portteus is leaving immediately for personal reasons.