This was revealed by her husband, Jun Santiago, on Thursday, GMA News reported.
Her official Facebook page also released a statement.
Earlier this month, it was reported that she was being treated for her cancer at the St. Luke's-Global City.
It was in July 2014 when Santiago announced that she had been diagnosed with Stage 4 lung cancer.
Despite her condition, she was able to run for the presidency in the recently concluded May elections.
However, it was evident during the debates that she was suffering health-wise as she was stuttering while delivering her answers.
Although Santiago placed dead last among the six presidential candidates, she still enjoyed massive approval from the supporters of the other candidates, especially from then Davao City Mayor Rodrigo Duterte's camp.
Santiago has been a senator for three terms (1995–2001 and 2004–2016), was a judge of the International Criminal Court (2012–2014) and served as the late president Corazon Aquino's secretary of Agrarian Reform (1989–1990).
Here is a short video to remember her colorful personality by: