CARACAS, Venezuela (AP) -- Venezuelan President Hugo Chavez is heading back to Cuba on Sunday for more surgery for cancer, announcing on television that the illness has returned after two previous operations, chemotherapy and radiation treatment.
Chavez acknowledged the seriousness of his situation in an address Saturday night, saying for the first time that if he suffers complications Vice President Nicolas Maduro should take his place as Venezuela's leader and continue his socialist movement.
"There are risks. Who can deny it?" Chavez said, seated at the presidential palace beside Maduro and other aides.
"In any circumstance, we should guarantee the advance of the Bolivarian Revolution," Chavez said.
Outside medical experts said that based on Chavez's account of his condition, he is facing a very difficult fight against an aggressive type of cancer.
The president, who just returned from Cuba early Friday, said tests had found a return of "some malignant cells" in the same area where tumors were previously removed.
Chavez, who has yet to be sworn in for his new term after winning re-election on Oct. 7, said he would return to Havana on Sunday and would undergo the operation in the coming days.
Chavez's quick trip home appeared aimed at sending a clear directive to his inner circle that Maduro is his chosen successor. He called for his allies to pull together, saying: "Unity, unity, unity."
Chavez said his doctors had recommended he have the surgery right away, but that he had told them he wanted to return to Venezuela first.
"I want to go there. I need to go to Venezuela," Chavez recalled telling his doctors. "And what I came for was this," he said, seated below a portrait of independence hero Simon Bolivar, the inspiration of his Bolivarian Revolution movement.
Chavez named Maduro, his longtime foreign minister, as his choice for vice president three days after winning re-election. Maduro, a burly former bus driver, has shown unflagging loyalty and become a leading spokesman for Venezuela's socialist leader in recent years.
The vice president's expression was solemn as Chavez said that Maduro should become president if any complication were to prevent him from finishing his current term, which concludes in early January. Chavez said that if new elections are held, his movement's candidate should be Maduro.
"In that scenario, which under the constitution would require presidential elections to be held again, you all elect Nicolas Maduro as president," Chavez said. "I ask that of you from my heart."
Chavez held a small blue copy of the constitution in his hands and waved it. The Venezuelan constitution says that if a president-elect dies before taking office, a new election should be held within 30 days and that in the meantime the president of the National Assembly is to be in charge of the government.
While he spoke, Chavez was flanked by both Maduro and National Assembly President Diosdado Cabello.
Chavez is scheduled to be sworn in for a new six-year term Jan. 10, and he called his relapse a "new battle."
This will be his third operation to remove cancerous tissue in about a year and a half.
The 58-year-old president first underwent surgery for an unspecified type of pelvic cancer in Cuba in June 2011, after an operation for a pelvic abscess earlier in the month found the cancer. He had another cancer surgery last February after a tumor appeared in the same area. He has also undergone chemotherapy and radiation treatments.
Chavez said tests immediately after his re-election win had shown no sign of cancer. But he said he had swelling and pain, which he thought was due to "the effort of the campaign and the radiation therapy treatment."
"It's a very sensitive area, so we started to pay a lot of attention to that," he said, adding that he had reduced his public appearances.
Chavez made his most recent trip to Cuba on the night of Nov. 27, saying he would receive hyperbaric oxygen treatment. Such treatment is regularly used to help heal tissues damaged by radiation treatment.
Chavez said that while he was in Cuba tests detected the recurrence of cancer.
He arrived back in Caracas on Friday after 10 days of medical treatment, but until Saturday night had not referred to his health. His unexplained decision to skip a summit of regional leaders in Brazil on Friday had raised suspicions among many Venezuelans that his health had taken a turn for the worse.
"I hope to give you all good news in the coming days," said Chavez, who held up a crucifix and kissed it. "With the grace of God, we'll come out victorious."
Dr. Carlos Castro, scientific director of the League Against Cancer in neighboring Colombia, told The Associated Press that he expects the operation will likely be followed by more chemotherapy.
"It's behaving like a sarcoma, and sarcoma doesn't forgive," Castro said, adding that he wouldn't be surprised if the cancer had also spread to the lungs or other areas.
"We knew this was going to happen," he said. "This isn't good."
Throughout his treatment, Chavez has kept secret various details about his illness, including the precise location of the tumors and the type of cancer. He has said he travels to Cuba for treatment because his cancer was diagnosed by doctors there.
Dr. Michael Pishvaian, an oncologist at Georgetown University's Lombardi Cancer Center in Washington, said in a phone interview that he wasn't surprised by the news.
"I think this is recurrent cancer that at this point is almost certainly not going to go away," Pishvaian said. "It's unlikely that what he's going through now is curable."
He speculated that given what Chavez has said about his cancer, it is most likely a soft-tissue sarcoma. He said those in the pelvis area have a likelihood of recurring of 50 percent to 70 percent, even with the best treatment.