When Dr. Beth Sieling first started out as a breast surgeon in 2004, decisions about how to treat breast cancer were based largely on a patient’s age, the size and grade of the breast tumor, and whether the cancer had spread to lymph nodes or elsewhere in the body.

Dr. Beth Sieling, division chief of Breast Surgery,  St. Mary’s Hospital

“We treated women without knowing much about how their tumor might behave,” says Sieling, division chief of Breast Surgery at St. Mary’s Hospital in Waterbury, Connecticut. “The treatment really wasn’t individualized. Two tumors might have appeared to be the same clinically but were completely different cancers genomically, acting in completely different ways.”   

Back then, when two women with identical-looking breast cancers received the same treatment, one might thrive and the other might not. And doctors didn’t know why.  

How things have changed. Today, thanks to the development of advanced testing known as tumor genomic assays, women with breast cancer can receive highly individualized treatment targeted specifically to the gene activity of their breast tumor.

“This testing gives us information about how the tumor might behave in the future, whether it’s High Risk, Low Risk, or very Low Risk for relapse, and whether or not chemotherapy and endocrine therapy will benefit that patient,” Sieling says. “Genomic assay testing allows us to avoid overtreatment or undertreatment.”

How big a deal is genomic assay testing for breast cancer patients?

“This has completely changed the paradigm of breast cancer treatment,” Sieling says. “It’s a huge, huge leap. It’s the biggest step since I’ve been in practice, and I’m so happy to be able to offer it to my patients.” 

Highly personalized treatment

When Sieling performs a biopsy or lumpectomy on a patient’s breast tumor, she has tissue from the tumor tested using MammaPrint® and BluePrint® genomic assays. These tests, which are provided by Agendia, Inc., a world leader in precision oncology for breast cancer, evaluate breast tumor tissue to determine the activity levels of certain genes.  

MammaPrint analyzes 70 genes within a tumor to predict whether the breast cancer may recur. It classifies breast cancer as having a High, Low, or Ultra Low risk of recurrence. BluePrint analyzes 80 genes within a tumor to determine what is driving its growth. It uncovers previously unknown information about tumor biology, including how tumor cells may respond to treatment. 

An important point for patients to know: Genomic assays, which offer insights into the potential behavior of a tumor and inform treatment planning, are different from genetic tests on a patient, which look for the presence of mutations in specific genes related to hereditary breast cancer, such as BRCA1 and BRCA2.

 Benefits to patients

Breast cancer is typically treated with surgery to remove the cancer and one or more lymph nodes. In addition, patients may receive chemotherapy, radiation therapy, and/or endocrine therapy. Endocrine therapy is a type of treatment that interferes with the activity of hormones that are known to drive the growth of some breast cancers. Common endocrine therapy drugs include aromatase inhibitors and tamoxifen.

In the past, doctors didn’t always know who would likely benefit from chemotherapy and endocrine therapy and who would not. But thanks to MammaPrint and BluePrint, doctors now have more information to determine whether these treatments will help individual patients.

 “Now, we’re able to spare many women chemotherapy who would have received it in the past,” Sieling says. “We know whether or not it will benefit them. That’s amazing.”

Dr. Sieling has many experiences of MammaPrint and BluePrint results influencing patients’ treatment plans in a positive way. For example, she recalls a patient of hers who was diagnosed with invasive breast cancer at the age of 40. Her tumor was positive for estrogen and progesterone (meaning it grew in response to these hormones) and negative for HER2 (a receptor that affects cell growth). The patient also had a cancerous sentinel lymph node.

Standard of care therapy for a young patient like this with a positive lymph node would typically include chemotherapy. “But she had the MammaPrint and BluePrint done, and guess what? She was Low Risk Luminal A,” Sieling says. “Instead of chemotherapy, her medical oncologist recommended an aromatase inhibitor with ovarian suppression. She had a second opinion from an oncologist who is a leader in the field, and he agreed with the treatment plan. She was spared chemotherapy, and now, three-plus years after her diagnosis, she is doing fabulously.”

Avoiding side-effects

Why not just give chemotherapy, a standard five-year course of endocrine therapy, and five additional years of extended endocrine therapy to every patient? Because these treatments have some major potential side effects. Chemotherapy may cause hair loss, fertility problems, and damage to the heart and nerves. Endocrine therapy can lead to years of hot flashes, night sweats, vaginal dryness, loss of libido, bone loss, and joint pain.

Doctors can prescribe various drugs that help relieve some of these side-effects. But even so, they can still have a major impact on a patient’s quality of life.

“When the benefits outweigh the risks, sure, we should absolutely use these treatments,” Sieling says. “But there’s no reason to recommend them to patients who are not going to get any benefit from them.”

 MammaPrint and BluePrint also help determine how long patients should stay on endocrine therapy drugs. Some benefit from 10 years of endocrine therapy; others can do just as well taking it for five years or even fewer than five years. 

 “It all comes down to treating the individual patient in a way that will benefit them the most,” Sieling says.

A pandemic boon 

During the worst part of the COVID-19 pandemic, MammaPrint and BluePrint gave doctors an additional, unexpected benefit: They helped physicians determine which breast cancer surgeries could be postponed, and which ones absolutely had to be performed as soon as possible. 

“For a while, our operating rooms were closed to all but the most urgent cases,” Sieling recalls. “But I was able to tell some of my patients that they could safely wait for surgery. I felt very comfortable with that, because I could base those decisions on the results from MammaPrint and BluePrint. Those tests really helped us during COVID.”

Empowering breast cancer patients

Sieling believes every breast cancer patient should have genomic assay testing. She orders MammaPrint and BluePrint testing for all of her patients because the results provide the information necessary to make truly informed decisions about treatment. 

“With all that information in front of us, we can make decisions that are right for each individual,” Sieling says. “I believe in shared decision-making between doctors and patients, and this testing makes the choices clear. I love that, because patients feel very empowered when they can make their own educated decisions.”