While there’s a lot of breathless talk about the potential of big data to do just that, Greg Simon, the Executive Director of the White House’s Cancer Moonshot Taskforce, is a skeptic—at least for now.

“What big data?” asked Simon speaking at Fortune’s Brainstorm Health conference in San Diego Wednesday. “We have in the health system, what is basically insider trading. I know something you don’t know. You know something I don’t know. When I need to know what you know, I call you, I email you. You fax me stuff.”

He continued: “Big data is the big yellow object that everyone is in love with. But we still live in an information scarce medical world.” He noted that while the U.S. has a database of every stock transaction dating back to the 1920s, many patients can’t even liberate their own personal medical records.

His organization is one of many working to make medical data free (or freer). And of the Genomic Data Commons, a database introduced in June to pool genomic and clinical data and make it available to researchers, he reports modest success. The Commons now holds the raw genomic data, from the Cancer Genome Atlas, of 32,000 people—up from 14,000 at its June launch (it will soon be several hundred thousand people). And that data has been accessed 5 billion times since June.

Simon qualified that as “the good news.” The bad? When the government launched the Cancer Genome Atlas, it spent $100 million to get data from 50,000 people. Of that, data from 24,000 people was unusable, he said.

“So big data is in the middle of bad data—which is being created by a lack of pathology and medical standards, and the lack of ubiquitous, instant data transmission like we have with financial and weather data,” Simon said.

He added of big data’s prospects in tackling cancer: “Can it make a difference? Yes. But we have to change the culture of sharing information, because our ability to share has far outpaced our attitude about sharing it.”