Cancer, the antagonist of this book, is the uncontrolled growth of abnormal cells in the body, which can end up killing a person afflicted with cancer. Cancer affects all four of main characters in The Fault in Our Stars. Hazel is a long time cancer patient with stage 4 Thyroid cancer. Augustus is a cancer survivor who had his leg amputated to get rid of his cancer, but despite this, he later gets cancer all through his body and dies thanks to this disease. Isaac was forced to have his eyes removed-leaving him blind- because of his cancer. Peter Van Houten lost his daughter at age 6 to leukemia.