If you’re wondering why some of your Facebook friends are posting pictures of their dogs to some kid named Anthony, here’s why.

16-year-old Anthony Lyons has acute lymphoblastic leukemia, and he’s currently undergoing rounds of chemotherapy at the Phoenix Children’s Hospital. According to his mother, Kristen, one of the highlights of Anthony’s days in the hospital are when he gets visits from dogs.

But the animal therapy isn’t as consistent as he’d like.

With the help of some friends, Kristen set up a Facebook “event” called Photo Doggies for Anthony. All she asked was for people to post photos of their dogs (and the occasional cat), along with some well wishes for Anthony.

And the thing blew up. I mean, it really took off.

As of right now, there are over 800,000 people “attending” the event, and according to the page, over a half a million photos have already been posted.

“I am amazed at how quickly this event has blown up and it makes me so happy to know how many people enjoy their pets as much as Anthony and I do,” said Kristen on the event page. “Your pets have brightened our days so much and it just shows you the power of pet thearapy and animal healing. This just shows what great people animal lovers are and we are really feeling the love from you and your pets in this difficult time.”

“When I’m in the hospital bed all day my mom goes through all the pictures, she sees them all,” Anthony told FOX 10. “She’ll show me them all, doesn’t matter, but the special ones are the funniest ones.”

If you want to help with the family’s medical bills, this GiveForward page is the place to go. If you want to post a cute photo of your puppy and some get better soon wishes, well, that’s free.

Image via Giveforward, Anthony’s Journey to Wellness