Precision Medicine + Metastatic Breast Cancer

What is precision medicine and why does it matter when treating Stage IV breast cancer?

If you’ve already heard of precision medicine, what you’ve read likely fell into one of two camps. One point of view: it’s our ticket to sci fi-style healthcare. On the flipside, it’s an interesting tool, but certainly not the healthcare revolution we’ve been hoping for.

It’s a complicated topic, and we’re just at the very beginning of understanding how precision medicine will change healthcare, and breast cancer treatment in particular. But we do know that the truth isn’t as black and white as Wired’s perspective vs. The Atlantic’s. So, here are four things you need to know about precision medicine, and why it’s especially relevant for metastatic patients.

It’s really about targeted treatments.

The key to precision medicine is data—when doctors can identify exactly what tumour markers are specifically causing someone’s cancer, it’s easier to develop a targeted treatment.

Under our current system, each disease has a “standard of care,” or treatment protocol that is determined by scientific studies and survival stats. (In oncology, each type, stage and grade of the tumor has a standard of care.) There’s a reason medicine works this way—it’s an evidence-based approach where treatments have been studied and proven to work for most people, most of the time. If that first-line treatment doesn’t work for you, there are second- and third-line options that are also based on stats and outcomes.

Precision treatments help make therapy more customized. Doctors can now analyze the genes found in a tumour to look for the mutations that can cause cancer and often prescribe drugs that target cells with that mutation, destroying them and leaving healthy cells alone. Women with stage IV HER2-positive breast cancer, for example, may be prescribed trastuzumab (Herceptin), which binds itself to the HER2 receptors in a tumor cell and blocks them from receiving growth signals, which then slows or even stops the tumor from growing.

When it comes to precision medicine research, breast cancer is one area of healthcare with lots of potential—but it’s still early days.

In the breast cancer world, genetic testing is familiar territory. We already know that women with BRCA1, BRCA2 or PALB2 mutations have a higher risk of developing breast cancer. And targeted treatments, like Herceptin, already exist. But while we’re already pretty far along compared to some other diseases, there’s still far to go. Researchers are currently trying to identify other mutations and, more importantly, the drugs that target them.

Instead, doctors may just need a blood test to determine exactly what medication a person’s cancer will respond to—and what it won’t. This doesn’t mean just fancy new targeted treatments, by the way. A genetic test might reveal that your cancer will respond best to chemotherapy, or a combination of chemo and a targeted drug.

Either way, time is one of a metastatic patient’s most valuable resources, and this approach has the potential to save a lot of time.

Some of the benefits (like progression-free survival and better quality of life) are particularly important for women with metastatic breast cancer.

Precision medicine won’t just improve survival rates for women with metastatic disease. In fact, in the short term, the benefits are likely to be incremental. But those small improvements include an important impact on quality of life, since patients won’t have to try treatments their cancer may or may not respond to—and similarly, won’t have to suffer through side effects for medication that may not.

This might seem like a small victory, but quality of life is particularly important for metastatic patients. They don’t have time to waste—they’re living with a disease that will shorten their lifespans and eventually kill them. But the hope is that targeted therapies can keep their health stable so their focus can stay where it belongs: on spending time with loved ones and their own emotional well-being.

But there’s a serious economic downside to precision medicine, and we have to address it before some women are excluded from the benefits.

Precision drugs are only part of the story, but they’re an important one. Some combination treatments, which combine targeted drugs and chemo, have shown really promising results — one study found pertuzumab (Perjeta), chemotherapy and trastuzumab can extend life by 16 months, a massive amount of time for women with metastatic breast cancer. It’s true: these drugs are expensive. Developing them costs a lot of money, as do the clinical trials that are necessary to get them approved for use in Canada. But to the women with metastatic breast cancer, to whom more time is so valuable, they are also worth the cost.

Up next: we delve into exactly why cancer drugs, from targeted therapies to traditional chemo, are so expensive.

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