The Minnesotan behind Cologuard, which fueled the biggest health care acquisition of 2025

When the late Dr. David Ahlquist visited the streams of southern Minnesota with his Mayo Clinic colleagues, the trips would always transcend flyfishing and nature hikes.

Driving back and forth to these waters, Dr. Richard Goldberg said his colleague would brainstorm how scientists could separate human DNA from bacterial DNA. This challenge, if solved, would allow doctors to noninvasively detect colon cancer without a dreaded colonoscopy.

Now Cologuard, which Ahlquist co-invented, is everywhere.

Last month it was at the center of the year’s biggest health care transaction announcement, a deal worth more than $23 billion that includes the transformational technology to detect colon cancer without a colonoscopy. The test’s maker, Madison-based Exact Sciences, says it detects 92% of colon cancers, even in early stages. A newer version increases the detection rate to 95%.

Illinois’ Abbott Laboratories is acquiring Exact Sciences. Kevin Conroy, the Cologuard maker’s CEO, said Ahlquist was a remarkable person whose contributions helped revive the company.

“He was just a complete human being,” Conroy said in an interview. “He was an athlete. He was an intellect... He understood science in such a deep way.”

Since the U.S. Food and Drug Administration granted Cologuard approval in 2014, people have used the self-administered stool test to screen for colon cancer more than 23 million times. It detects cancer markers in the DNA contained in stool.

Cologuard’s broad adoption alone didn’t satisfy Ahlquist toward the end of his life, his former colleagues say. A larger challenge emerged: Could Cologuard’s technology detect a wide array of cancers?

Dr. John Kisiel, who now runs Ahlquist’s Mayo lab, said, “It was not daunting to him. It was daunting to everyone else.”

Ahlquist, diagnosed with ALS in 2019, was in a race against time.

The idea that detecting colon cancer earlier could cut the disease’s mortality rate fueled Ahlquist’s passion for researching it when he was a young scientist at Mayo.

By the mid-1990s, Dr. Paul Limburg, Exact’s chief medical officer for screening, said Ahlquist understood that using tests identifying blood in stool to detect cancer wasn’t enough. While having blood in stool is associated with cancer, Ahlquist turned to DNA to find genetic markers that directly indicate abnormal cells in the colon, Limburg said.

Some gastroenterologists approached Ahlquist’s ideas at first with “at least skepticism and perhaps hostility,” Goldberg said. They felt it would take away from their work performing colonoscopies. Ahlquist argued the opposite, Goldberg said: Positive stool tests would lead to additional colonoscopies.

By 2009, Ahlquist’s team had landed on the panel of DNA markers that now power Cologuard.

The Mayo Clinic team, though, would need a business partner. Without marketing and sales forces, academic institutions often do not commercialize their technologies on their own.

At the time, Exact Sciences was looking for a lifeline to stay in business. Dwindling to just a couple of employees, it had tried to develop its own stool DNA test — twice — and failed.

When the board of directors at Exact asked Conroy to become CEO and spearhead the company’s turnaround around 2009, he at first declined. Then a board member asked, “before you say a definitive ‘no,’ would you go meet with Dave Ahlquist?”

Ahlquist presented the rough start to a test. He successfully laid out the case that Cologuard could potentially eradicate colon cancer if everyone screened frequently enough, Conroy said.

Instead of just acquiring Mayo’s intellectual property, Exact struck a deal to collaborate with Ahlquist, funding his lab and salary with the understanding that the company would pay royalties to Mayo if the technology was ever commercialized.

For decades, Ahlquist’s research had sent him to northern Alaska to study the higher rate of anemia and colon cancer in Alaskan Natives. Limburg joined and said his colleague approached the work “with enthusiasm, with respect, with dignity for the people.” A longtime relationship formed that would prove vital for Conroy’s company.

Meanwhile, clinical trials using a refined version of Ahlquist’s original ideas were showing such positive results that company officials had applied to the FDA for approval by 2014.

Executives had expected regulators to quickly green-light Cologuard following an initial clinical trial, Conroy said. Despite outperforming scientific expectations, the agency requested a second study, Conroy said — which the CEO assumed the company didn’t have.

“We would not have been possible without Dave,” Conroy said. “Now, it wouldn’t have been possible without some other people. But Dave is the first person.”

After Cologuard, Ahlquist wasn’t done. And his 2019 ALS diagnosis wouldn’t stand in his way.

William Taylor, the principal research technologist in the doctor’s lab, said Ahlquist approached life with the spirit of an adventurer: “He was an avid cross-country skier. He’d go hiking in the Arctic. He would take roads and get lost.”

Ahlquist described his ALS diagnosis to Exact’s Limburg as an “adventure.”

Limburg explained, “It shows how Dave accepted and embraced anything that came his way.”

“It’d be the sort of the Holy Grail,” Taylor said, “to have a test [that] would tell you if you have cancer somewhere in your body, and then you can kind of figure out where it is from the test.”

Dr. Kisiel, who runs Ahlquist’s lab, said the physician had decided a wider test would require many more biological markers than Cologuard used.

The team’s work to discover those genetic markers was well underway when Ahlquist died.

Exact launched Cancerguard in September, nearly five years after his death. The company reports it can detect more than 50 types and subtypes of cancer including pancreatic, ovarian, liver, esophageal, lung, and stomach forms of the disease from a blood sample.

“I think he would be delighted to see what’s happened,” said Goldberg, who explored the southern Minnesota streams with Ahlquist as he thought up Cologuard in the 1990s.