(UPDATE) MANILA - Senator and presidential hopeful Miriam Defensor Santiago will be skipping the second leg of the next Commission on Elections (Comelec) presidential debate on Sunday, citing health reasons.

In a statement issued Thursday, Santiago said she will undergo a clinical trial for a "new, unnamed anti-cancer pill" on March 20, the same day of the Comelec-initiated debate scheduled in Cebu City.

"I am very sorry to miss out on the debates, but it would be a disservice to the country if I forego the opportunity to get rid of my cancer completely and strengthen myself further to serve the Filipino people," Santiago said.

This is contrary to her statement back in October 2015, when she announced her intent to run for president and claimed to have conquered cancer.

The lawmaker has always been positive about her health, even saying that "nobody dies of cancer anymore as long as you have the money."

Santiago on Thursday said she volunteered to be part of an international clinical trial to be able to get hold of the medicine, which reportedly costs half a million pesos for every three weeks of treatment.

The clinical trial also requires the senator to undergo outpatient radiation treatments.

Santiago added she will try her best to attend the third and last presidential debate happening on April 24, "if the ongoing treatments do not inhibit" her.

ABS-CBN and Manila Bulletin will host the Luzon leg of the Presidential debate next month at the University of Pangasinan in Dagupan City. The debate will use the Town Hall format.

Santiago was diagnosed with stage 4 lung cancer in June 2014. She took a break from the Senate but later announced she will be running for president and has since delivered speeches mostly in universities, where she is popular among millennials.

Santiago, who has not been seen much in political sorties, is banking on her online popularity in her quest to win the presidential elections.