Obama signed many landmark bills into law during his first two years in office. He left to attend graduate school on a scholarship at Harvard University, where he earned an M.A. in economics. Obama chose to stay in Hawaii with his grandparents for high school at Punahou when his mother and half-sister returned to Indonesia in 1975 so his mother could begin anthropology field work. His mother spent most of the next two decades in Indonesia, divorcing Lolo in 1980 and earning a PhD degree in 1992, before dying in 1995 in Hawaii following unsuccessful treatment for ovarian and uterine cancer.Obama later reflected on his years in Honolulu and wrote: 'The opportunity that Hawaii offered—to experience a variety of cultures in a climate of mutual respect—became an integral part of my world view, and a basis for the values that I hold most dear.'