New liquid biopsy threatens Exact – or does it?

After a terrific tear across 2017 during which its share price nearly quadrupled, it was perhaps inevitable that fate would catch up with Exact Sciences. Fate has arrived in the shape of Taiwanese company Cellmax Life, whose liquid biopsy for colorectal cancer appears to put Exact’s Cologuard in the shade.

An abstract released ahead of the Asco-GI meeting this week showed that Cellmax’s test was able to detect colorectal cancer with accuracy comparable to Cologuard’s, and Exact’s stock duly fell 10% yesterday. But Cellmax’s trial set a low bar, and it is years behind Exact; it still has a great deal to prove.

At first glance the data are damning for Exact. Comparing the Asco-GI data on Cellmax’s circulating tumour cell (CTC) blood test with data from Cologuard’s pivotal US trial, Deep-C, indicates that CellMax CTC beats Cologuard on every measure except the sensitivity with which it detects colon cancer.

An unfair comparison: CellMax CTC vs Cologuard
CellMax CTC* Cologuard**
Sensitivity (cancer only) 87% 92%
Sensitivity (precancer only) 77% 42%
Sensitivity (cancer or precancer) 84% Unknown
Specificity 97% 87%
*Asco-GI data, **Pivotal trial (Deep-C) results

CellMax CTC’s superior precancer sensitivity might be particularly galling for Exact given that its own miss on this metric caused its shares to crash 30% when it was revealed in 2013 (Exact Sciences braces for fallout from Cologuard’s precancer miss, April 18, 2013).

But cross-trial comparisons are always risky, and the designs of these trials were so different that this one is riskier than most.

Cellmax specifically enrolled cancer and precancer patients – 438 of them – and a control group of 182 healthy people. In Deep-C, Exact’s test was used the way screening tests are intended to be used in the real world – in other words, in a general population of middle-aged and older people. This is a much trickier setting.

Deep-C tested 9,989 patients, only 65 of whom (1%) had colonoscopy-confirmed cancer, and 757 (8%) precancer. These rates were 53% and 18% in Cellmax’s study. The Cellmax trial was much smaller, and conducted at a single site in patients aged 20-plus – hardly representative of the real-world screening population.

Shorts dropping

If the sensitivity and specificity of CellMax CTC hold up in later, larger studies then yes, Exact will definitely have a fight on its hands. The Taiwanese test involves a blood draw rather than sending a faecal sample for testing, and with Cellmax suggesting it could sell for $100-150 versus Cologuard’s price of around $500 it could indeed nab much of Exact’s market.

But obtaining approval will involve multi-year trials in tens of thousands of patients, and even after that it will likely take several more years to lure payers away from Exact. Use of Cologuard as a screen is covered by Medicare and Medicaid plus all the major insurance companies in the US, and Exact had to work very hard indeed to get it to that position (Smaller medtechs soar in ’17 but could now be too expensive, January 10, 2018).

Competition is not a worry for Exact, and neither is revenue growth. And the startling expansion of its market value seems to have scared off the bears: short interest in its shares was tracking at around 24% a year or so ago but at the end of 2017 this proportion had fallen to just 7%. If the shorts are looking to Cellmax to rescue them they will have a long wait.

To contact the writer of this story email Elizabeth Cairns in London at elizabethc@epvantage.com or follow @LizVantage on Twitter

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