Last week's news about Herceptin made quite a splash, and there are several reasons for that. The main one is the correct one: this is good news for breast cancer patients, and a real advance in the treatment of the disease. The other reasons for all the excitement may not be quite as justifiable, though. In short, while this is significant, it's a long way from a cure.
Herceptin (trastuzumab) is an antibody targeted to a growth factor receptor called HER2 (more background from a previous post here, and from Genentech here. Those are the short version and the long version, more or less). If the cancer doesn't express HER2, it will not respond to Herceptin. The more dependent the tumor is on HER2 for its growth, the better the antibody will work, which is a common theme among cancer therapies. (An extreme version is found with Iressa, where if the tumor doesn't have the rare mutation that makes it dependent on the drug's targets, it doesn't work at all).
So, how many breast cancers express HER2? There are several ways to assay that, and the numbers disagree a bit, but a bit under 20% seems like a reasonable answer. Put more harshly, for about 80% of breast cancer patients, herceptin is of little or no use. This has been proven quite thoroughly, but it's going to be hard to explain to patients who are newly diagnosed and want to know where that cure is that they've read about.
I haven't seen any headlines that have tried to explain that these results are good news for only a certain group of breast cancer sufferers. Many of the press reports get around to mentioning this eventually, although rarely in the first paragraphs - you wonder how many people are still reading when they get to the fine print. The fine print, in this case, would include the numbers that show a twelve per cent increase in disease-free survival after three years. That's big news in oncology, but isn't generally the kind of number that you makes you throw around the word "cure". I hope that some of the people in these news stories have been quoted out of context.
It's true that by the time you add up the taxanes, the estrogen receptor ligands like Tamoxifen, the aromatase inhibitors, and the general advances in surgery and early detection, that breast cancer is a less fearsome disease than it was five (or ten, or twenty) years ago. But advances in this area get overhyped because - and I hate to bring this up - the disease itself is overhyped. Don't get me wrong - it's bad. But it's far from the worst.
The rate of breast cancer, like many other cancers, appears to be declining (PDF), measured both by incidence and by death rate. It's well behind that of lung cancer in the female population, which moved into first place nearly 20 years ago (see the graph on page 5 of this PDF), but it gets easily ten times the press, and surely generates ten times as much worry. Lungs, though, are not visible manifestations of femininity, and come with no cultural or political meaning attached. I'm sure that there's a ribbon color for lung cancer, although I don't know what it is, and I don't know when their Awareness Month might be. This is especially odd when you consider that most of the high incidence of lung cancer is from a completely avoidable cause. . .
(I see that Medpundit has a very similar take on this: "Don't sell the house" is her advice.)