UPDATE 7/15: Thanks to Reddit, the entire 4th Floor had a pizza party yesterday. Pic at the bottom.
Hazel, nicknamed "Hazelnut", was diagnosed with a High-Risk, Stage 3 Neuroblastoma on April 24, 2013 and is now receiving 18 months of treatment at Children's Hospital in Los Angeles. Earlier today, with the help of her family, she used tape to put up a sign in her window reading "Send Pizza" along with her room number. The sign was spotted by a Redditor who posted it to the site. Within an hour it made the front page where it was seen by millions and many, many pizzas were ordered. If you want to help the family in a different way (as they're surely sorted for pizza about now), you can read more about Hazel here.