A new study claims that breast cancer is not a single disease, but an umbrella term for four different types of cancer that have different survival rates and require different kinds of treatment.
In a new study published in the Journal of the National Cancer Institute, a group of researchers from the North American Association of Central Cancer Registries (NAACCR), the American Cancer Society, the Centers for Disease Control and Prevention (CDC), and the National Cancer Institute (NCI) says breast cancer is composed of four subtypes that are distinct from one another at the molecular level.
The researchers say classifying breast cancers into four subtypes can help medical researchers ascertain the origins of the diseases and allow health practitioners to develop better treatment plans for each subtype.
"This is a welcome step, depending on medically important information that already guides therapeutic strategies for these subtypes," says Harold Varmus, director of the NCI, in a statement. "The new diagnostic categories now being defined will increasingly support our ability to prevent and treat breast and many other kinds of cancer, as well as monitor their incidence and outcomes more rigorously over time."
Analyzing the incidence of invasive breast cancer in women in 2011 from data obtained from the member registries of the NAACCR, the researchers have classified the four subtypes according to their hormone receptor status, or the status of a chemical receptor lying in breast cancer cells that reacts to hormones, such as estrogen. The classification also considered the expression of the HER2 gene. Using this method, the researchers classified breast cancer into the following subtypes: Luminal A (HR+/HER2-), Luminal B (HR+/HER2+), HER2-enriched (HR-/HER2+), and triple negative (HR-/HER2-).
The researchers believe that the existence of different breast cancer subtypes is closely related to the differences in cancer mortality rates across various ethnicities and across different ages, poverty levels, and geographic areas within the same ethnicity.
For instance, the incidence of triple negative breast cancer, which is the most aggressive of all subtypes, was found to be higher in non-Hispanic black women, which coincides with the highest mortality rate due to breast cancer in blacks. They were also reported to have higher rates of late-stage breast cancer.
On the other hand, Luminal A breast cancer, the least aggressive among the subtypes, is most common in non-Hispanic whites. The researchers also discovered that the incidence of Luminal A decreased with a decline in poverty levels among all races and ethnicities.
Varmus calls the new classification of breast cancer a "harbinger of the more rigorous classification of cancers based on their molecular features." Cancer registries across the nation are now recording these subtypes to help statisticians examine breast cancer figures based on "clinically meaningful" subtypes.
Photo: Brandy Gill, CRDAMC PAO | Flickr
