* Thompson became prime minister in January 2008
* Deputy Stuart in charge for now
* Thompson has dual role as Barbados finance minister (Adds Thompson's expected to return to Barbados, background)
By Robert Edison Sandiford
BRIDGETOWN, Sept 17 (Reuters) - Barbados Prime Minister David Thompson has been diagnosed with pancreatic cancer, an often fatal illness, and is receiving medical treatment in the United States, his doctor said.
The illness, which has thrown Thompson's leadership into doubt, was disclosed by his personal physician, Dr. Richard Ishmael.
The cancer was confirmed during the 48-year-old Thompson's recent visits to New York for medical treatment, Ishmael said in a statement on Thursday.
Thompson had announced in July that he was taking two months of medical leave and traveling outside the Caribbean island, leaving his attorney general and deputy, Freundel Stuart, in charge of the former British colony of 286,000 people.
The prime minister returned to his official duties, but Ishmael said he had been forced to fly back to New York because of a thrombosis, or blood clot, in the vein surrounding the pancreas.
Thompson, who leads the ruling Democratic Labour Party, took office in January 2008.
The prime minister also serves as finance minister in Barbados, which won independence in 1966 and has overcome the decline of its once-powerful sugar industry to grow relatively wealthy through high-end tourism, light industry and offshore financial services.
Pancreatic cancer often has a poor prognosis. It spreads rapidly and is seldom detected in its early stages, which is a major reason why it is a leading cause of cancer death.
Although his medical condition has left Thompson tired and thinner, Ishmael said, he was able to fulfill his duties as prime minister "at a reduced pace."
Ishmael said Thompson had returned to New York on Sept. 6 and had been undergoing chemotherapy at New York-Presbyterian Hospital. The blood clot is apparently dissolving and the prime minister is expected back in Barbados sometime next week, he said.
In the event Thompson is unable to complete his five-year term, Senate President Branford Taitt said, the governor-general would decide on a successor before elections in 2012.
"I would think that Freundel Stuart is the natural choice," said Taitt, considered the ruling party's elder statesman.
When Prime Minister Tom Adams died in office in 1985, Bernard St John, his deputy, was appointed prime minister.
St John lost to Errol Barrow in the subsequent 1986 general elections. When Prime Minister Barrow died in office in 1987, Erskine Sandiford, his deputy, was appointed premier after a brief challenge from within the party. Sandiford went on to win the 1991 general elections. (Editing by Tom Brown and Mohammad Zargham)
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