How a Life-Changing Trial is Transforming the Lives of Metastatic HER2+ Breast Cancer Patients

As a 20-year mammographer, 72-year-old Catherine Mulqueen often encountered patients at their most vulnerable. And she was always proactive about her own healthcare, especially because her cystic breasts made potentially worrisome lumps hard to detect.

Mulqueen stayed current on mammograms until 2010 when her husband, Michael, became gravely ill with renal cell carcinoma. When she developed a painless breast lump, she shooed it aside, being busy working full-time and supporting Michael through his treatments.

“I put it into the back of my mind,” she recalls.

After Michael passed away, Mulqueen, then 57, could consider her own health.

A mammogram, ultrasound, and core biopsy close to her York, Maine, home revealed that she had stage III, HER2+ invasive ductal carcinoma. HER2+ breast cancers tend to be aggressive and without treatment, are more likely to spread.

It was the beginning of a journey that would both showcase her resilience and challenge the perceptions of metastatic, HER2+ breast cancer as an incurable disease. 

An unexpected recurrence

Because of the size of her cancer, in October 2010, Mulqueen had a right mastectomy and lymph node surgery. Next, she began a standard regimen of chemotherapy with a monoclonal antibody called trastuzumab, commonly known as Herceptin. A targeted therapy for HER2+ breast cancer, Herceptin can reduce the risk of death by a third and cut the risk of relapse in half. (Nowadays, Lin notes, she would have been started with chemotherapy and trastuzumab prior to having surgery).

Mulqueen also underwent radiation. She experienced side effects — hair loss, fatigue, and dehydration — but after 12 weeks, Mulqueen was back at work, providing other patients mammograms. She was her usual unflappable self.

“I tend to be a fairly optimistic person, and I just took it in stride,” she says.

Life settled down until May 2013, when Mulqueen’s grown children made a disturbing observation.

“My adult son and daughter kept saying to me: ‘Mom, you’re asking me the same question over and over.’ I said, ‘All my friends are turning 60. We’re doing too many things. We don’t remember things. We’re multitasking,’” she recalls. 

Yes, she was fatigued. Sure, she had some headaches. She figured it was just part of aging, not a cancer recurrence. While HER2+ breast cancer can spread to the brain, this is rare: less than 5 percent of patients experience brain metastasis as the first location of cancer spread.

Still, at her local oncologist’s urging, Mulqueen underwent a brain MRI. It revealed a tumor in her brain, requiring emergency brain surgery. A follow-up PET scan revealed that she also had liver metastasis. At this point, Mulqueen was classified as having metastatic breast cancer.

From breast cancer to patient advocate

From Maine, Mulqueen sought a second opinion from Nancy Lin, MD, founder and director of the EMBRACE (Ending Metastatic Breast Cancer for Everyone) Metastatic Breast Cancer Program and the Program for Patients with Breast Cancer Brain Metastases at Dana-Farber. With Lin’s counsel, she began a regimen of Herceptin and pertuzumab, known as Perjeta, a monoclonal antibody that blocks HER2 and targets breast cancer cells in the liver.

HER2-targeted therapies such as trastuzumab and pertuzumab significantly improve survival in metastatic breast cancer, Lin says, although they don’t cure the disease.

“When cancer is metastatic, the current paradigm is that we give lifelong treatments to control the cancer,” Lin explains.

Historically, the survival for patients with cancer that has spread to the brain was only about 6 months. Happily, Mulqueen has remained stable on her treatment for several years without recurrence. 

“Initially, I thought that I’d probably live maybe a year. I’d never see my children get married. But my daughter got married in 2019. I was here for my first and second grandson being born,” she says.

Eager to share her story, Mulqueen decided to give back. She became a patient representative for EMBRACE, a Dana-Farber program offering educational resources and support to patients. In 2019, she traveled from Maine to speak at an in-person forum with newly diagnosed women. They were reassured to see Mulqueen, living with optimism and strength after more than a decade with the disease.

“Catherine is incredibly generous. A lot of people who came to the forum were newly diagnosed, and it was so powerful to see someone doing well with good quality of life. At the time, she was still coming in every three weeks for treatment. She’s just the sweetest, kindest person,” Lin says.

The chance for a cure

In 2022, witnessing Mulqueen’s exceptional response, Lin had a suggestion. She told Mulqueen about the STOP-HER2 clinical trial, based at Dana-Farber. In this phase 2 trial, patients who had responded well to anti-HER2 treatment could either continue or stop therapy while being monitored with regular scans and bloodwork. The trial could identify which patients might safely discontinue treatment entirely and whether some could be cured. 

Because Mulqueen had experienced more than three years without cancer progression, she was an excellent candidate.

“For so many years, we’ve thought of metastatic breast cancer as an incurable disease. While we need to follow patients long-term, it turns out that there’s probably a group of patients that we’re actually curing. They won’t need to be on treatment for the rest of their lives,” Lin says. “This is completely changing the mindset around what is possible in people who have HER2+ metastatic breast cancer.” 

Mulqueen was intrigued. The treatment she was on at the time came with side effects. She’d soldiered on, true to form, but she would have welcomed a break. She was also proud to give back to the cancer community, and enrolling in a trial could help future patients.

On the other hand, the prospect of stopping treatment was frightening.

Mulqueen opted to continue standard treatment. Still, she remained open-minded. In February 2024, she saw Lin again. The trial was still ongoing. This time, with her children’s encouragement —and eager to shed side effects that kept her from playing with her young grandchildren — Mulqueen was ready to give STOP-HER2 a try.

And so she joined the trial in March 2024 and has shown no disease progression since beginning. Overall results of the trial are expected in December 2026.

“It’s a tremendous act of courage to enroll in this trial, because it really is jumping into the unknown,” Lin says. “We tell people with metastatic breast cancer that we can’t predict the future. We take things one day, one month, one year at a time.”

Mulqueen was initially monitored for disease every three months through bloodwork, brain MRIs, and CT scans of her chest, pelvis, and abdomen. Thanks to Mulqueen’s excellent response, she will soon switch to scans every four months instead of three, and then stretch to six months. 

Best of all, she feels more energetic, and her side effects are minimal. She can care for her toddler grandkids. And now, she’s happy to share her story as a clinical trial patient.

“The best is, the neuropathy in my hands is so much better. My fingertips were so numb that I could barely close the little snaps on my oldest grandson’s onesies. Now, I have no problem at all. It’s just incredible,” she says. “Each day is a joy.”