What is the true meaning of "I want to eat your pancreas"?
So, this relates to the fact that in Japanese culture, and various other Asian cultures as well, mothers use a phrase along the lines of 'I will eat up your disease X, so that you can get all better...' to their children; the title here refers to the fact that,


  Haruki wants Sakura to get all better from the disease she is suffering, which is some sort of pancreas disease