An emotional Bonino told Radio Radicale that the tumour was discovered on her left lung during routine checks.
“It is treated as localized and still without symptoms, but nonetheless it will require long and complex chemotherapy treatment that has already been started and will last at least six months,” she said.
Although not wanting to put an end to her political career, Bonino said her medical needs must be an “absolute priority” at the moment.
“I am not my tumour and nor are you your illnesses; we must only think that we are people that face a challenge that arises,” she went on to say, while asking for the media to respect her privacy.
Italy reacted with sadness to the news, with #ForzaEmma (“Have strength Emma”) soon trending on Twitter.
Before Monday's announcement, Bonino was tipped to take over from President Giorgio Napolitano, who formally announced his resignation in December. Politicians are yet to decide upon his replacement, although many have said that Italy should appoint its first female president.
Until the fall of Enrico Letta's government in February last year, Bonino served as Italy's foreign minister. The 66-year-old was first elected to parliament in 1976 and has for decades worked in international affairs, including five years spent as EU commissioner for humanitarian affairs.
Listen to Bonino's announcement: