Now, with many diseases, including most cancers, you can also look at disease prevalence, which is the total number of patients at any one time. Prevalence numbers will be larger than incidence numbers because it takes into account more than one year.
For the purposes of my model, I found finding prevalence figures for prostate cancer difficult, so I chose to use incidence. That's me being conservative, a stance I'll take throughout this model because I'd rather underestimate than overestimate.
Provenge, at least initially, will not be given to all prostate cancer patients. Instead, use will be restricted to patients who have metastatic, androgen-independent (hormone-refractory) disease, which means their cancer has spread beyond the prostate and it is no longer being controlled by hormone treatments. These patients will also be asymptomatic, which means they won't have any outward symptoms, such as bone pain, which could signal new growth of their cancer.
Here comes the hard part -- figuring out the percentage of prostate cancer patients who fit that category, which is labeled "AIPrC" in my model above. After a lot of Googling and research, including looking back at some old analyst notes, my best guess is that 35% of prostate cancer patients are no longer responding to hormone treatments. That's what I used in my revenue model to come up with a total population of AIPrC patients -- the target group for Provenge.
Not all eligible prostate cancer patients will choose to take Provenge. How many will? Frankly, this is an educated guess, especially since Provenge is a first-in-class cancer immunotherapy without precedent.
But again, after some research, I learned that about 65% of hormone-refractory prostate cancer patients choose to move onto chemotherapy treatment for their disease. Provenge, if approved, would slot between hormone therapy and chemotherapy, so for my modeling purposes, I decided to assume that the same 65% of patients would choose Provenge. Given the excellent side-effect profile of Provenge, this percentage might actually end up higher, but again, I like to be conservative.