I was confused this weekend when I read that the Cancer Genome Atlas Project, which has been precisely mapping the mutations in tumors, had found that breast cancer can be divided into four types. That seemed like an old story. Paul Raeburn at the Knight Science Journalism Tracker was also puzzled as he watched the meme spread through the news.
The official press release from the National Cancer Institute said the study “confirmed that there are four primary subtypes of breast cancer,” implying that the classification already existed. But the paper itself, published in Nature, said that it “demonstrated the existence of four main breast cancer classes.” Something was getting lost in the semantics.
For years women diagnosed with breast cancer have been told that their tumors are ER-positive, PR-positive, HER2-positive, or triple negative. What that means is that their malignant cells are producing an excess number of receptors for either estrogen, progesterone, or human epidermal growth factor — or that they don’t fall into any of those categories. Triple negative is another way of saying “none of the above.”
Digging a little deeper, I learned that for at least a decade researchers have been parsing the cancer more finely and now talk about molecular “subtypes”: luminal A, luminal B, HER2-enriched, and basal-like. Again there are four varieties but there is not a one-to-one correspondence with the more familiar list. Most triple-negative breast cancer has been found to be basal-like, but estrogen-positive cancers can be either luminal A or B.
The new study appears to go further. Cancers that test positive for HER2 do not necessarily fall into the same genetic category now called HER2-enriched.
At this point my head was spinning. The suggestion that there was a new classification scheme was apparently a red herring, unintentional I’m sure. The bigger news, which received less emphasis in most of the coverage, was that triple-negative/basal-like is remarkably similar to serous ovarian cancer.
This must all sound esoteric to anyone not dealing with breast cancer. But by providing more details about the four main paths the malignant cells can follow, research like this might lead someday to more effective treatments. It will take a long time, and there is no reason for difficult, nuanced science like this to be reported in such a rush. But that has always been the nature of the news business, and the pressure of the Internet has made it so much worse.