An American doctor stranded at the South Pole for five months with symptoms of breast cancer was rescued yesterday when a U.S. military plane picked her up at a remote research station.

The Air Force jet risked potentially hazardous weather conditions during the four-day journey to pick up Jerri Nielsen, 47, the only doctor at the isolated Amunsden-Scott research station.

Pilots had limited visibility, but landed safely at 7:33 p.m. EDT on Friday, using a runway the staff at the station had carved out of ice, U.S. Air Force spokesman Victor Hines reported from Christchurch, New Zealand.

With the temperature hovering around 58 degrees below zero, pilots kept the four propeller engines of the LC-130 Hercules running to keep them from stalling. In the 22 minutes the plane was on the ground, Nielsen was carried on board and a temporary replacement doctor was left at the research station.

Planes typically wait until later in October when the weather has stabilized at 50 degrees below zero before attempting routine flights to the barren station, where about 40 researchers and support staff live in a geodesic dome half buried by snow.

But an Air Force medical evacuation team began planning the October trip as soon as Nielsen discovered a lump in her breast this summer.

After days of unpredictable polar weather, the plane left McMurdo's Station on Antarctica's coast for the 6 1/2 hour round trip, becoming "the earliest flight into the South Pole in the history of the program," said Maj. Bob Bullock, spokesman for the 109th Airlift Wing of the Air National Guard.

"This mission carried elevated risk because of the potential extremes of weather," said Bullock, speaking from Saratoga Springs, N.Y., where the plane originated. "From the very outset it was treated with a special focus. Nothing was left to chance."

Nielsen arrived at the research station almost a year ago for what her mother, Lorine Cahill, has described as an adventure. Nielsen had just ended a 24-year marriage, and left three teenage children behind with her former husband.

When she signed up to be resident doctor, Nielsen was opting for a life of isolation: nine months of basically unbroken darkness, freezing temperatures and a landscape of nothing but snow. Planes cannot land during the polar winter for fear that the fuel might crystallize and their landing gear freeze.

In early July, Nielsen discovered a lump in her breast and alerted the National Science Foundation, which operates the base. Because she was the only doctor on the base, Nielsen prepared to treat herself.

On July 11, an Air Force jet did an emergency drop of medical supplies, imaging equipment and sophisticated teleconferencing equipment. Linked by satellite to oncologists in the United States, Nielsen performed the biopsy and treated herself.

Physicians who have consulted with Nielsen have told officials at the National Science Foundation that her condition is not immediately life threatening, said foundation spokesman Peter West. They would not release any more details about her illness.

But Nielsen has e-mailed pictures of herself to friends and family that show her losing her hair from chemotherapy, her mother and ex-husband said.

She is expected to fly through New Zealand and arrive in the United States for treatment, although spokesman would not disclose her final destination.