A New Category of Breast Cancer Means New Possibilities

At the American Society for Clinical Oncology (ASCO) conference earlier this year, a new breast cancer drug received a standing ovation after researchers announced the results of their trial. This drug is Enhertu, and it was recently approved by the FDA to treat people with a certain type of metastatic breast cancer. VBCF doesn’t tend to report on specific drugs for breast cancer treatment because treatment is so individualized – one treatment that works wonders for one person could be ineffective for another. The reason Enhertu warrants some discussion is that it essentially creates a new type of breast cancer that can be a new research focus: HER2-low.

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To understand the potential impact of this new distinction, here’s a simplified explainer of breast cancer types. Breast cancer isn’t just one disease, but can be divided into (previously) four basic types. 

HR+, or hormone receptor-positive breast cancer, means that the tumor has receptors for estrogen and/or progesterone, two hormones that are usually abundant in a biological woman’s body. These receptors were discovered and subsequently targeted for treatment, improving outcomes for people with HR+ breast cancer. HER2 is a protein that some breast cancer tumors express, and in 1998 the drug Herceptin, which targets HER2, was approved to treat metastatic HER2+ breast cancer and then early-stage HER2+ in 2006. Again, the identification of the protein created a target for medicine which in turn dramatically improved outcomes for people with HER2+ breast cancer. The final category is triple-negative breast cancer, which means the tumor isn’t positive for estrogen, progesterone, or HER2. This breast cancer subtype accounts for 10-15% of diagnoses, but carries a 40% mortality rate in the first five years, and is more common in younger women and women of color. 

When someone undergoes testing for their breast cancer, their tumor can be analyzed to see to what extent it is HR or HER2 positive. In order for a tumor to be considered HER2+, it needs to “score” a 3+ on the HER2 test.  However, some people have their HER2 results come back at 1+ or 2+, so they aren’t considered HER2+, but they aren’t negative either and are considered “HER2-low.” Because they don’t fit the benchmark for HER2+, many of these people end up in the triple-negative category. 

Here’s where Enhertu comes in. It was approved specifically to treat people who have HER2-low metastatic breast cancer, and is the first drug to have been approved for this subtype. But this is not why the drug received a standing ovation: it’s because that, during trials, Enhertu reduced the risk of disease progression or death by 50% and increased overall survival by six months. When it comes to metastatic breast cancer, these numbers are huge. This is why the FDA acted so fast to approve the drug. We’ll see in the coming years how the real world results compare to the trials, but it’s off to an encouraging start.

In addition to the impact on the lives of individuals with breast cancer, what are the implications of Enhertu’s success and approval? Maybe we will differentiate between people who are diagnosed with HER2-low breast cancer and “true” triple negative. Maybe we’ll learn more about who is more likely to be diagnosed with HER2-low, and more trials will be created focusing on that population. Hopefully, this means that more treatments will be developed that will improve the lives and reduce breast cancer deaths in younger women and women of color.

If you are interested in learning more about clinical trial participation, visit our clinical trials page.





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