Fernando Lugo, the president of Paraguay, has been diagnosed with a type of cancer known as lymphoma, although his doctors said he has a good chance of being treated successfully.
The doctors said on Friday that a biopsy carried out this week showed Lugo had non-Hodgkin's lymphoma, but said it was treatable because it had been caught in its early stages.
"Early studies carried out on the gland taken from President Fernando Lugo showed the existence of a malignant illness called lymphoma," Jose Ballesai, one of his doctors, said at a news conference in the capital Asuncion.
Esperanza Martinez, Paraguay's health minister, said that the president would continue official business as normal.
Lugo, a former Roman Catholic bishop who left the church to run for office, is due to travel to the Brazilian city of Sao Paolo next week for consultations on the course of further treatment.
His doctors said chemotherapy may be recommended to treat the cancer.
Lugo, 59, underwent surgery earlier this year to treat a swollen prostate.
The president has been under pressure recently at home over a spate of murders and kidnappings blamed on a small armed group operating out of the country's remote north.
His term as president is set to expire in 2013.