Hi Gregory, Thank you for helping try to establish these probabilities. I am not sure I follow the math (I'm not used to doing these calculations). Could you explain how you calculated it? Thanks again!

I attempted to contact them, but they did not reply. These are top Crohn's researchers, and must be very solicited from all sides, so their lack of response is expected.

(2b) (2c) (2d) are being run right now by different groups. I don't know how long it will take for them to publish (best guess ~1-2 years).

What numerical value do you assign to the probability of replication of Samuel et al 2010 (variable X)?

Hi Hauke, Thank you very much for this suggestion. Yes, animal models would be another category 2 option. You might know that Barry Marshall had much trouble developing animals models of Helicobacter pylori-induced gastritis, so this approach is hit-and-miss at best, and it is hard to know ahead of time what the probability of a "hit" would be. It is also less ethical than the other solutions, and for this reason, I'd prefer avoiding animal models (if possible).

Hi Gregory, here are some more options:

X = odds that Samuel et al 2010’s results will replicate (range 0 - 1).

Category 1 options: studies which can bring X’s value close to 1.

(1a) A well powered RCT testing itraconazole in Crohn’s (success = curing Crohn’s).

Category 2 options: cheaper studies which can increase X, but not bring it close enough to 1 to change clinical practice. However, they would raise awareness that Crohn's might be caused by a fungus, and thus might be cured by itraconazole. Hopefully someone will do (1a) based on the results of these category 2 options.

(2a) Test Samuel et al 2010 by using a larger medical database than that available at the Mayo Clinic in 2010 (ideally in the mid-West where histoplasmosis is endemic).

(2b) Antibodies against Malassezia are associated with psoriasis (Squiquera et al 1994; Liang et al 2003). We could try replicating these studies in Crohn's disease.

(2c) In psoriasis, white blood cells release interferon gamma when exposed to Malassezia antigens (Kanda et al 2002), likely because T cells are specifically targeting Malassezia on the skin. We could replicate this study in Crohn's disease.

(2d) We could replicate Kellermayer et al 2012 or Richard 2018, who found extremely strong associations between Malassezia and IBD.

Note that (2c) will likely be successful because vedolizumab is known to cause psoriasis in ~10% of Crohn's patients by sending T cells from the gut to the skin (Tadbiri et al 2018).

Other ideas are welcome!

Hi Gregory, Great suggestion! The main issue with this approach is that it seems long-term use of itraconazole is required (>3 months), which rarely occurs in practice. Most on-label uses of itraconazole are for much shorter periods, which is one reason why Samuel et al 2010 was such an exception: histoplasmosis is only prevalent in the mid-West, and requires a very long course of itraconazole.

A second problem is that once treatment is discontinued, Crohn's symptoms seem to return after a few months (again per Samuel et al 2010). This is very much like dandruff (caused by the fungus Malassezia): once antifungal shampoos are discontinued, Malassezia return, and so does dandruff! So we'd have to be able to test using the medical database if these Crohn's patients got a flare or not during the treatment period (as compared to properly selected controls - getting comparable/unbiased controls using this methods is not trivial).

In addition, Samuel et al 2010 was very well positioned to detect the effect of itraconazole, because they stopped giving their patients immunosuppressants - so they were expecting severe flares during treatment. This is not expected to occur in most cases from medical databases.

Finally, I don't think medical database studies like this can be used to change medical practice. Would the FDA allow a new indication without an RCT? I doubt it. So running a database could not reach the stated impact.

How many patients do you think we would need in a RCT to have sufficient power? The researchers I am working with think itra=20, placebo=20 would be sufficient. I don't have the expertise to evaluate this. Samuel et al 2010 noticed a marked effect on 5 patients, although there were no controls, so they were judging this using their clinical experience. FWIW, the last author of Samuel et al 2010 is one of the top Crohn's researchers in the world.

Hi Zeke, Thanks for the clarification and the estimate for Y. If I understand correctly:

(1) Minimum success probability for project viability is ~0.5% (Y=0.5%)

(2) Upside following success is 33B$*10 years = 330B$ (per your earlier estimate, this needs to be adjusted for many different reasons, both up and down, but these adjustments are beyond my capabilities).

(3) Cost is 500K$.

(4) Expected ROI is = (330B$ * 0.5%) / 500K$ = 3300.

So this means if you find a 100$ bill on the sidewalk and giving it away to someone else statistically gives them ~300K$, you will keep it, but if it statistically gives them 400K$ you will give it away. Is that right?

Thanks, very much appreciated! I will ask Mati to change the summary.