The Fault in Our Stars: What is a spoiler? Why would Hazel be concerned about them?

The plans are made for Augustus, Hazel, and Hazel's mother to go to Amsterdam, but when Hazel and Augustus meet Van Houten they find that, instead of a prolific genius, he is a mean-spirited drunk who claims he cannot answer any of Hazel’s questions. The two leave Van Houten’s in utter disappointment, and accompanied by Lidewij, who feels horrified by Van Houten's behavior, they tour Anne Frank’s house. At the end of the tour, Augustus and Hazel share a romantic kiss, to the applause of spectators. They head back to the hotel where they make love for the first and only time. The following day, Augustus confesses that while Hazel was in the ICU he had a body scan which revealed his cancer has returned and spread everywhere. They return to Indianapolis, and Hazel realizes Augustus is now the grenade. As his condition worsens he is less prone to his typical charm and confidence. He becomes vulnerable and scared, but is still a beautiful boy in Hazel’s mind. As this change occurs, she ceases calling him Augustus and starts referring to him as just Gus, as his parents do. Hazel recognizes that she loves him now as much as ever. Augustus’s condition deteriorates quickly. In his final days Augustus arranges a prefuneral for himself, and Isaac and Hazel give eulogies. Hazel steals a line from Van Houten about larger and smaller infinities. She says how much she loves Augustus, and that she would not trade their short time together for anything in the world.Augustus dies eight days later. Hazel is astonished to find Van Houten at the funeral. Van Houten explains that he and Gus maintained correspondence and that Augustus demanded Van Houten make up for ruining the trip to Amsterdam by coming to his funeral to see Hazel. Van Houten abstractly reveals the fate of Anna’s mother, but Hazel is not interested. A few days later Isaac informs Hazel that Augustus was writing something for her. He had hinted about writing a sequel to An Imperial Affliction for her, and as Hazel scrambles to locate the pages she encounters Van Houten once more. He drunkenly reveals that Anna was the name of his daughter. She died of cancer when she was eight, and An Imperial Affliction was his literary attempt at reconciling himself with her death. Hazel tells Van Houten to sober up and write another book.