Discovering I had bone cancer when I was only 12 forced me to mature very quickly. Doctors found a growth about the size of an orange in my pelvis, after a pain in my left leg got really bad over the summer of 2014.

The diagnosis was osteosarcoma. Surgery is usually a part of the treatment. But because the tumor was so close to some vital nerves, almost every doctor my parents consulted recommended amputation. If I’d stayed in...