The developer behind the moving indie game That Dragon, Cancer--which chronicled a family's struggle with childhood cancer--has spoken up to say Let's Play videos for the game affected sales negatively. In a blog post, lead developer Ryan Green--the father of 5-year-old Joel Green who has since passed away--said his studio Numinous Games "has not yet seen a single dollar from sales," and Let's Play videos may be partially to blame.

"That Dragon, Cancer was created by a studio of eight, and for many of us it was a full-time effort that involved thousands of hours of work," he said. "This huge effort required taking on investment, and we decided to pay off all of our debt as soon as possible. But we underestimated how many people would be satisfied with only watching the game instead of playing it themselves. And so yes, Let's Play person, I agree with you, it does suck to have someone else making revenue off your work."

Green cited SteamSpy data, which suggests That Dragon, Cancer has sold around 14,500 copies on Steam.

Millions of people have watched That Dragon, Cancer videos on YouTube, Green said, and this could have eaten away at game sales.

"We have seen many people post our entire game on YouTube with little to no commentary," he said. "We've seen people decompile our game and post our soundtrack on YouTube. We've also seen many, many Let's Players post entire playthroughs of our game, posting links to all of their own social channels and all of their own merchandising and leaving out a link to our site."

This isn't to say that Green takes issue with the Let's Play movement overall. "We've watched the playthrough videos and we see the value that this community is adding to our work through sharing themselves. Let's Play culture is vibrant and creative and really cool," he said.

Another issue was that video creators reported being handed copyright claims after Numious added Content IDs to for composer Jon Hillman's music. There should be no issue around this going forward.

"We have removed all of our Content IDs from Jon's music. If anybody received flags for ad revenue share, you should be able to reupload in a few days without the flag," he said. "We did not intend to make copyright claims or to force anyone to take down their videos, we simply intended for Jon to be able to draw some income from the original soundtrack to our game that he poured his heart into."

Green went on to say that, had just a fraction of viewers left a $1 tip, the situation around That Dragon, Cancer as it relates to sales could have been a different story.

"All we are asking in return is that you honor our work, the work you build your livelihood on top of, and acknowledge that when you do it, there is a real cost to developers," he explained. "For us, it costs us the ability to continue to share this game through translation into other languages and bringing it to new platforms, along with starting new projects."

Going forward, Green said he hopes people who create Let's Play videos for That Dragon, Cancer do not just rebroadcast gameplay with minimal commentary. Instead, he would like to see people use snippets of gameplay as "context to share your own stories and start conversations with your viewers." He also said he hopes Let's Play streamers add a link to the That Dragon, Cancer website and encourage viewers to donate to the studio if they can. "This small act will allow us to continue to work," he said.

Green also said in his blog post that, excluding these Let's Play issues, things have gone very well for him and the team. The response to That Dragon, Cancer has been incredible and confounding, he said.

"The last few months since we launched That Dragon, Cancer have been pretty incredible," he wrote. "The mainstream culture, the gamer culture, and others have all embraced our story and been willing to listen to our heart as we released a project that we spent more than three years on. They're talking about Joel and sharing their own stories of loss and bringing comfort to each other. In every regard, the reach of our work continues to confound us."

GameSpot's That Dragon, Cancer review scored the game a 9/10.

"It's virtually impossible to not bring one’s own biases into That Dragon, Cancer, because death and disease are universal," reviewer Justin Clark said. "Just as it's impossible to quantify whether the exploration of those two heavy topics is worth the time and considerable emotional energy, it's impossible to truly quantify the immeasurable value of being able to not just forever present the best version of a person to the world, but being able to earn his presence in every way his parents did."