But Kristin Hallenga has refused to let it break her spirit. Despite her ordeal, she has focused her energy on helping others combat the disease.
In a Cancer Research UK ad, Kristin touched millions of hearts as she said: "Cancer isn't a fight we always win".
She has also launched a campaign, Coppa Feel, to ensure young women recognise breast cancer signs.
In February, Kristin, who has an identical twin Maren, was found to have cancer in her breast and spine. Yet eight months earlier a GP told her not to worry about her "lumpy breasts".
She has had radiotherapy and chemotherapy and now faces surgery.
But she remains upbeat and wrote on her blog: "I'm only 23 and staring at the prospect of a hairless, boobless life. It is my highest hope that by sharing my story, other young women will learn a potentially lifesaving lesson."