As a researcher at Memorial Sloan-Kettering Cancer Center, Lois Murphy helped develop pioneering treatments for children suffering from leukemia and other cancers at a time when such a diagnosis was almost always fatal. Murphy, who died April 8 at 91, was a pediatric oncologist at the cancer center for four decades, including 11 years as chairwoman of the pediatrics department. Her work is credited with developing therapies that brought the survival rates for many childhood cancers to 70%. Previously, treatments were unsystematic and survival rates were in the low single digits.

“She played a key role in developing combination therapies,” the center’s chairman of pediatrics, Richard O’Reilly, said. “That became something that radically changed the history of lymphomas in kids.”

Murphy developed a national system for coordinating pediatric clinical trials, and instituted the center’s day hospital, a pioneering program in which young patients are administered chemotherapy on an outpatient basis.

Born on a western Nebraska cattle ranch, Murphy was raised in a sod house and as a girl rode a horse three miles to a one-room schoolhouse. Her father carved gravestones for a living. The family moved to Lincoln, where Murphy became the first in her family to attend high school. Her homeroom teacher was Elsie Cather, sister of Willa, and Murphy later credited her teacher with helping to introduce the concept of socializing, after years on the lonely plains.

Murphy attended the University of Nebraska, and continued on in the graduate chemistry program, where she was the only woman. She graduated in 1944 from the university’s medical college after an accelerated wartime program. She was one of only two women in her class. “There wasn’t any discrimination,” she told the medical college’s alumni association recently. “Often, other students were gracious enough to carry my microscope.”

The same couldn’t be said of the school itself, which refused to hire female interns. Instead, Murphy became a resident at a pediatric hospital in Philadelphia. She worked closely with a young pediatric surgeon named C. Everett Koop. According to one story, she decided to reorient her career toward clinical research after treating an entire high school football team stricken with polio. She stood but 5 feet tall.

In 1951, Murphy accepted two fellowships in New York, one in experimental chemotherapy at the Sloan-Kettering Institute, and the other in medicine at the Memorial Hospital for Cancer and Allied Diseases. She was one of the few researchers at that time to focus on childhood cancers. Murphy organized tests of new anticancer drugs in animals and then in clinical trials on children. In 1958, she became chairman of the Acute Leukemia Group A, later the Children’s Cancer Study Group, a national clearinghouse for children’s clinical trials. She was named chairwoman of pediatrics at the Memorial Sloan-Kettering Cancer Center in 1965. To help sick kids lead more normal lives, she introduced the day hospital in 1968. By 1974, it was receiving 12,000 visits annually and the concept spread across the country.

Among her patients in the early 1950s was 3-year-old Robin Bush, the leukemia-stricken daughter of George H.W. Bush. “Despite the best treatment, she lived only five or six months,” Murphy recalled in the alumni association interview. “Nobody lived any longer than that until the mid-1960s.” She remained friends with the Bushes, and was invited to the inauguration of President Reagan in 1981.

Another celebrity patient was Shelley Bruce, who had starred in the musical “Annie” on Broadway before being diagnosed with acute leukemia in 1981.

“She was this tiny ball of energy and life,” Ms. Bruce, who stayed friends with Murphy, said. “I didn’t know how instrumental she was in those breakthroughs. I just knew she saved my life.”

Mary Lois Murphy

Born in 1916 in Sioux County, Neb.; died April 8 at her home on the Upper East Side; never married, she is survived by several nieces and nephews.