Ginsburg, 75, has been a justice since 1993. She has been increasingly vocal in recent years about the court's more conservative stances, especially after the appointments made by President George W. Bush.
Pancreatic cancer is often deadly, although the court said doctors apparently found Ginsburg's growth at an early stage.
In 1999, she had colon cancer surgery, underwent radiation and chemotherapy, and never missed a day on the bench. Statistics suggest this could be a tougher fight.
Ginsburg had the surgery at the Memorial Sloan-Kettering Cancer Center in New York. She will remain in the hospital for seven to 10 days, said her surgeon, Dr. Murray Brennan, according to a release issued by the court. The hospital had no comment.
The justices hold their next private conference on Feb. 20 and return to the bench from their winter break on Feb. 23.
President Barack Obama expressed hope for her speedy recovery, White House press secretary Robert Gibbs said Thursday, and offered his thoughts and prayers.
Ginsburg is only the second female justice in the nation's history. The other was Sandra Day O'Connor, who retired in 2006, and Ginsburg has lamented being the only woman on the court.
In the spring of 2007, she vented her frustration with the court's increasingly conservative tone by writing two sharp dissents that were made even more notable by her decision to read from them in the courtroom.
Objecting to a decision that upheld a nationwide ban on an abortion procedure that opponents call partial-birth abortion, Ginsburg said the ruling "cannot be understood as anything other than an effort to chip away at a right declared again and again by this court - and with increasing comprehension of its centrality to women's lives."
A short while later, the court threw out a discrimination suit by Lilly Ledbetter, a longtime Goodyear supervisor who was paid thousands of dollars a year less than her male peers. "In our view, this court does not comprehend, or is indifferent to, the insidious way in which women can be victims of pay discrimination," Ginsburg said.
She urged Congress to change the law to allow lawsuits like Ledbetter's. Just last week, Obama signed the change into law.
Ginsburg was born in New York City. She's a lover of opera and is perhaps personally closest on the court to her ideological opposite, Antonin Scalia. The justices have vacationed together - a photo in her office shows the two atop an elephant - and routinely mark New Year's Eve with an elaborate meal prepared by their spouses.
Ginsburg was a federal appeals court judge in Washington before President Bill Clinton appointed her. She served as a lawyer for the American Civil Liberties Union before that and argued six cases before the high court.
The new cancer was discovered during a routine, annual exam late last month at the National Institutes of Health in Bethesda, Md. A CAT scan revealed a tumor measuring about 1 centimeter across at the center of the pancreas, the court said.
The court offered few details about the operation or her anticipated course of treatment.
Pancreatic cancer is one of the most deadly cancers. Nearly 38,000 cases a year are diagnosed and overall less than 5 percent of patients survive five years.
The reason: Fewer than one in 10 cases are diagnosed at an early stage - like Ginsburg's appears to be - before the cancer has begun spreading through the abdomen and beyond. That's because early pancreatic cancer produces few symptoms other than vague indigestion.
Even when caught early, surgery for pancreatic cancer is arduous. Doctors typically remove parts of the pancreas, stomach and intestines. Radiation and chemotherapy are common after surgery.
Ginsburg's prognosis depends on a number of factors, including whether the tumor, despite its small size, had begun spreading to the lymph nodes, and what specific type it was. Most are aggressive, although a small proportion of patients have what Dr. John Marshall, a pancreatic cancer specialist at Georgetown University Hospital, calls "quieter ones."
"We want to be in that early group so we can have the surgery and have a potential chance at cure, but it is a big operation and a disease that does tend to spread even very early," he cautioned.
Even those few patients who qualify for surgery seldom are cured by it. So chemotherapy is standard to extend survival, which is still only about 20 percent at five years for people diagnosed in early stages.
Studies are under way to try to find better therapies. Among them: testing if an immune therapy can block the return of tumors that contain a specific genetic mutation.
Brennan, her doctor, is a leading specialist on pancreatic and stomach cancers and has helped to build a computer program and database of thousands of patients with sarcomas, or soft-tissue tumors, that help to predict their survival chances for at least 12 years after diagnosis.
Brennan was chairman of Sloan-Kettering's surgery department from 1985 until June 2006 and is past president of the American Surgical Association.
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