Replies to post #141999 on Biotech Values

[DewDiligence]

Re: Cumulative sensitivity of EXAS ColoGuard (or any other repeated diagnostic)

[Dew]: …a non-invasive, no-prep test such as EXAS’ ColoGuard can be repeated often, allowing the cumulative sensitivity of a series of tests to be impressively high for both cancer and pre-cancer even when the sensitivity of each individual test is only middling.

[iwfal]: That's only true if the individual tests are largely independent - and I'd bet they aren't.

I think independence of the individual tests is a reasonable first-order approximation. The DNA missed in any individual test depends on: i) the state of the GI tract at the time of the sampling; and ii) the error-prone physical handling of the stool sample by the patient. These factors can be expected to have a fairly high degree of random noise, bolstering the argument for the independence of individual tests. This is not to say that the issues you raised about differential shedding by different types of tumors and pre-cancerous lesions are not relevant, but rather that they are likely outweighed by the sampling randomness described above.

So [EXAS management] are either ignorant or disingenuous (not good either way).

That’s unduly harsh, IMO. EXAS management has not strongly emphasized cumulative sensitivity during investor presentations, but rather cited it as an ancillary benefit of a non-invasive test and they have generally mentioned it only in reply to a specific question from an analyst. I think this is good approach for management to take insofar as the SAP of the DEEP-C study on which EXAS’ prospects hinge do not include any calculations relating to cumulative sensitivity.

In short, the concept of cumulative sensitivity will not help EXAS succeed in the DEEP-C study, but it will (IMO) boost commercial uptake of ColoGuard if the product is approved by the FDA for marketing as a kit.

[DewDiligence]

EXAS…it would seem to be extremely difficult to equate Cologuard statistics with colonoscopy statistics since the former is probably about detecting any polyp/tumor, but the former is about detecting any individual polyp/tumor.

I cannot parse your statement as written—please restate.