premise: The surgery to remove a malignant tumor from the abdomen of Brazilian Vice President Jose Alencar was successful, said a medical team on Tuesday.
  Alencar felt well after the six-hour operation, said his spokesman, noting the vice president was still at the Memorial Sloan-Kettering Cancer Center in New York, the United States, undergoing after-surgery medical procedures. The center is regarded as one of the best oncology institutes in the world.
  Alencar is expected to be off duty till Dec. 7, but he planned to return to Brazil on Nov. 25.
  The tumor was detected on Oct. 30 shortly after he was elected vice president along with President Luiz Inacio Lula da Silva for another four-year term.
   Why did Alencar have the surgery?
hypothesis: The surgery to remove a malignant tumor