(CNN) -- Venezuelan President Hugo Chavez is battling cancer. Health problems began to pop up for him a year ago. Here are some key dates, according to government statements, local media accounts and CNN reporting:
May 9, 2011 -- Chavez calls in to Venezuelan state television and says that he's canceling a scheduled trip to Brazil because of debilitating pain in his knee requiring doctor-ordered bed rest.
June 5-7, 2011 -- Chavez visits Brazil and Ecuador and heads to Cuba, scheduled as the third leg of an international trip.
June 10, 2011 -- Venezuelan government officials announce that doctors in Cuba performed emergency surgery on Chavez to treat a pelvic abscess.
June 23, 2010 -- Venezuelan government officials go on the offensive as media reports suggest Chavez could have cancer. In a Twitter post, Venezuelan Vice Foreign Minister Temir Porras said Chavez's enemies should "stop dreaming," adding that "the only thing that has metastasized is the cancer of The Miami Herald and the rest of the right-wing media."
June 29, 2011 -- Venezuela's government cancels a conference for Latin American leaders in the capital of Caracas because of Chavez's illness.
June 30, 2011 -- In a speech broadcast on Venezuelan state television from Havana, Chavez reveals that doctors have removed a cancerous tumor from his body. He does not specify what type of cancer he is battling.
July 4, 2011 -- Chavez returns to Venezuela after more than three weeks of treatment in Cuba.
July 16-23, 2011 -- Chavez undergoes his first cycle of chemotherapy in Cuba. Before leaving Venezuela, he delegates some of his power to Vice President Elias Jaua and Finance Minister Jorge Giordani.
August 1, 2011 -- The Venezuelan president appears on state television with a shaved head, telling viewers it is a sign that his cancer treatment is working.
August 7-14, 2011 -- Chavez undergoes a second cycle of chemotherapy in Cuba.
August 27, 2011 -- Chavez announces he will undergo a third round of chemotherapy in a military hospital in Caracas.
September 18-22, 2011 -- Chavez undergoes a fourth round of chemotherapy in Cuba.
October 16, 2011 -- Chavez travels to Cuba for medical tests.
October 20, 2011 -- After five days of medical tests in Cuba, Chavez says he's beaten cancer. "There are no malignant cells in this body. They don't exist," he says.
January 7, 2012 -- Chavez restarts his weekly Sunday television program and speaks for more than three hours.
January 13, 2012 -- Chavez speaks for more than nine hours during a State of the Union speech in Venezuela's National Assembly.
February 20, 2012 -- Rumors swirl on social media after journalist Nelson Bocaranda, without naming sources, writes that Chavez was in serious condition and doctors are treating him in Cuba. The report draws ire from Venezuelan officials. "Regarding the rumors, dirty war of swine," Information Minister Andres Izarra writes in a Twitter post.
February 21, 2012 -- While touring a tractor factory in Venezuela's Barinas state, Chavez announces that he will undergo surgery to remove a lesion from the same area where doctors removed a cancerous tumor from his body last year. He does not specify where the lesion was found, but says it was roughly 2 centimeters in diameter.
February 24-March 16, 2012 -- Chavez travels to Cuba for cancer surgery and treatment.
March 25-29, 2012 -- Chavez travels to Cuba for radiation treatment
March 31-April 4, 2012 -- The Venezuelan president undergoes a second round of radiation treatment in Cuba.
April 6, 2012 -- During a Holy Thursday Mass in his home state of Barinas, Chavez tears up at times as he discusses his struggle with cancer. "Christ ... give me life, because I still have things to do for the people and this country. Do not take me yet," he says.
April 7-11, 2012 -- Chavez undergoes a third round of radiation treatment in Cuba.
April 14, 2012 -- Venezuelan Foreign Minister Nicolas Maduro announces that Chavez will not attend the Summit of the Americas in Cartagena, Colombia.
April 26, 2012 -- Chavez returns to Caracas after 11 days of treatment in Cuba.
May 2, 2012 -- Chavez names 10 Venezuelans to a new Council of State, stipulated in the Venezuelan Constitution as the highest circle of advisers to the president. The timing of the appointments is significant, as speculation increases over who will succeed Chavez if he becomes too ill to govern, or if he dies.