It is thought that Hannah Powell-Auslam could be the youngest person ever to be diagnosed with what is considered to be an adult disease.
And surgeons have told Hannah that she will need further surgery after they discovered that her cancer had spread to a lymph node.
Hannah said: “How could this happen? I am only 10 years old.
“I did not even know what cancer was. I just kept crying and crying and couldn’t stop.”
Hannah was first diagnosed in April after she complained of itching in her left breast and her mother noticed a lump. Her parents took her to the doctor, and a small portion of the lump was sent for tests.
No one suspected breast cancer.
Hannah’s mother, Carrie Auslam, said: “They told me it was not breast cancer, because breast cancer does not happen to children.”
But Hannah was found to have a slow-growing invasive secretory carcinoma. Hannah, of Fullerton, California, said: “I just told my mum I want to be a normal kid. I want to go back to school, play sports, hang out with my friends.”
Doctors said she was the youngest to suffer the disease in the United States.
Dr Sarah Cant, of Breakthrough Breast Cancer, said: “Breast cancer is extremely rare in children, and of the nearly 46,000 cases of breast cancer in the UK in 2005, none was diagnosed in girls aged under 15.”