What is the theme in Shadowlands by William Nicholson?

Another theme in the book is pain and suffering. The other side of love and passion is pain and suffering. Lewis discovers that with love comes pain. It is only when Joy learns she is suffering from bone cancer, has a tumor in her breast, and breaks her hip that she and Lewis grow truly close and fall passionately in love. At first, Joy and Lewis believe she will die right away, but the disease's progression slows, giving them three years together. Hanging over this time is the inevitability of Joy's death. Both Joy and Lewis do not like the pain or the suffering. Joy, in particular, believes it is unfair that she becomes ill when she finds her soulmate.