The US National Institute of Health defines a disease as being “rare” if fewer than 200,000 Americans suffer from it. That said, there are 6,500-odd rare diseases, and about 25,000,000 people in the USA have one - about one person in twelve. If you know 600 people, chances are that about 50 of them have a rare disease. Clearly, the word “rare” here is being used in a different sense from what we’re used to!

The reason for classifying a disease as rare is pragmatic: even if you figured out a way to cure it, the cost of developing and testing the cure would be high enough that you would never make any money off it. Therefore, pharmaceutical companies can apply for special “orphan drug” status and get tax breaks, subsidies, and so on.
The word “rare” (or “uncommon”) in conjunction with IBC may well come from Susan Love’s Breast Book in the 1990’s (which has since been updated). The section on IBC was about half a page, and it said, roughly, that IBC was very aggressive with terribly grim statistics, but not to worry because you were unlikely to get it. (Obviously, this was not very comforting if you had just been diagnosed!) The actual incidence rate of inflammatory breast cancer is generally underreported, for three main reasons:
- IBC is a clinical diagnosis, not pathological, so it doesn’t always get reported in the right way to be counted.
- Some studies count IBC as any stage III(b) breast cancer, which discounts cases where it has already spread when it’s initially diagnosed, which would be classified as stage IV.
- Studies that count death statistics will generally see many more “metastatic breast cancer” cases than “inflammatory breast cancer”.
However, it is likely that the number of people with inflammatory breast cancer in the USA is at most 180,000, and possibly as low as 100,000. IBC is therefore officially classified as a rare disease, but only for the purposes of orphan drug subsidies. (Although the list of rare diseases on the government’s web site does not currently include IBC, that does not affect its actual status).
An aside: I’d love to organize a conference for IBC patients - maybe we’ll get about 200 people - and take a photograph of everyone together. It’s really hard to look at a picture of 200 people and think it’s rare, especially knowing that it’s only a tiny sample of the people who are diagnosed in a single year.
So there are three different meanings of the word “rare” as it applies to IBC:
- The Orphan Drug meaning: “under 200,000 people in the USA; not profitable”.
- The comparative meaning: “compared to breast cancer generally, not very many people get it”.
- The intuitive meaning: “It’s not going to affect me”.
Unfortunately, if you use the word “rare”, people automatically think “not important”. The perception of risk is a fascinating topic that I’ll be talking a lot more about, but the fact is that if you want someone to remember something important, telling them that it’s unlikely to affect them is a really bad start.
None of this would be important if IBC were the same as other kinds of breast cancer. But it’s not. It presents differently from other kinds of breast cancer, leading to frequently wrong diagnosis. The treatment protocol is different. The emotional issues patients face are different. The survival rate is vastly different, getting substantially worse with delays before treatment. The fact that it doesn’t affect as many people is less important than the fact that not knowing - either on your part or your doctor’s - could kill you.