Venezuelan President Hugo Chavez will officially register Monday to participate in the October elections amid growing speculation surrounding his health as he continues to battle cancer.

Chavez's sole challenger, Henrique Capriles, stepped down from his post as a state governor Wednesday and announced that he will formally enter his bid for the presidency on Sunday .

Capriles, 39, who is representing the center-right Justice First Party, is currently trailing Chavez, representing the far-left United Socialist Party of Venezuela, in national polls, though results vary from double-digit leads of 20 percentage points to only a few points.

Chavez, 57, has been in power since 1999. He will be running for his third six-year term as president since Venezuela established a new constitution in 2000 by public referendum.

For over a year, Chavez has traveled back and forth to Cuba for radiation therapy, though the Venezuelan government has been highly secretive regarding the president's health and specific details about his illness.

The severity and type of Chavez's cancer remains unknown, though a recent report from veteran journalist Dan Rather indicated that it could be in its terminal stages.

This reporter has been told that Venezuelan President Hugo Chavez has metastatic rhabdomyosarcoma, an aggressive cancer that has 'entered the end stage,' Rather said on the website.

The Venezuelan government has denied the report, saying Chavez is in a strong recovery and fit to run in the elections. Over the weekend, Chavez appeared vigorous and alert on Venezuelan state television.

What a lovely breeze, what lovely weather, he said, addressing government officials and a Belarussian delegation Saturday before delivering a lengthy speech on the front steps of the presidential palace, on topics that went from the Socialist revolution in Latin America to soccer.