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Patients with two of the three major types of advanced breast cancer now have a median overall survival of at least 5 years, which is roughly a doubling of survival time over the past decade, says an expert.

Collectively, patients with advanced breast cancers have “for a long time” had an average overall survival of about 2-3 years, observed Fatima Cardoso, MD, of Champalimaud Cancer Clinical in Lisbon, lamictal bone Portugal. She chaired a guidelines consensus panel at the Advanced Breast Cancer Sixth International Consensus Conference (ABC 6), held virtually earlier this month. The guidelines will be published in 2022.

Cardoso’s comments on survival in metastatic breast cancer were highlighted in a conference press release. She elaborated on those comments in an interview with Medscape Medical News.

The two types of advanced breast cancer where survival times have doubled over the past decade are HER2-positive (HER2+) breast cancer and ER-positive (ER+) breast cancer.

Survival data principally come from the two most important studies in these two cancer subtypes, the CLEOPATRA trial in HER2+ disease and the MONALEESA 2 trial in ER+ disease, she said.  

In CLEOPATRA, median survival was 56.5 months among HER2+ patients treated with first-line pertuzumab, trastuzumab, and docetaxel.

And in MONALEESA 2, median survival was 63.9 months among ER+ patients treated with first-line ribociclib and letrozole.

Cardoso’s claim about overall survival in metastatic disease is epidemiologic in nature. However, her assertion is based on data from clinical trials — and not cancer registries or other large, population-based data sets, as would be expected in epidemiology.

“We do not have good epidemiological data [for advanced breast cancer],” she explained about the use of clinical trial data sets.

That’s because most cancer registries worldwide, including in the United States, do not count relapses, and only register diagnoses and death. “If you want to know how many patients are actually living with metastatic breast cancer, you don’t know,” Cardoso observed.

Cardoso pointed out that data collection globally on metastatic breast cancer is changing and will eventually help researchers get a more accurate picture of survival.

The ABC Global Alliance, which sponsors the annual ABC conference, has, in the past few years, advocated for nations to start to tally recurrences, and thus, provide an accurate count of metastatic cases. Since then, France, Germany, and the Netherlands have established “real-world” metastatic breast cancer registries. The latest published results from Germany and France show a median survival of 3 years — for all subtypes. However, the considerably shorter survival for triple-negative disease pulls down the average, Cardoso told Medscape Medical News.  

Still, is it legitimate to make claims about overall survival, which apply to all patients including those in the “real world,” on the basis of results from two large clinical trials sponsored by drug companies, which tend to pick the most physically robust patients?

Cardoso countered that both the CLEOPATRA and MONELEESA trials did not have “a lot of restrictions” in terms of participants. One of the few restrictions was for women who had a “very short” period of time as early stage patients before progressing to advanced disease, which is an “uncommon” scenario, she said. Most patients with HER2+ or ER+ advanced breast cancer “would have been eligible for these trials and treatments,” she said.

“The big problem is that these treatments are very expensive — that is the biggest limitation. It’s not really the inclusion criteria of the trials — it’s accessibility,” Cardoso concluded.

Advances in Metastatic Breast Cancer

Cardoso noted that patients with HER2+ disease represent about 25% of patients with metastatic breast cancer and now commonly live as long as 10 years.

ER+ disease, which accounts for about 60% of metastatic cases, does not have quite the same success in clinical trials in terms of overall survival. But just this year, the combination of ribociclib and letrozole in the MONALEESA trial has been shown to improve overall survival on par with the improvements in HER2+ disease, she said.

Thus, for about 85% of metastatic breast cancer cases, median survival is 5 years, said Cardoso.

Thoughts About Other Types of Metastatic Breast Cancer

A continuing challenge is finding “some kind of treatment” that impacts the third major subtype, triple-negative disease, she said.

“We classify as triple-negative everything that we cannot classify as HER2+ or ER+,” Cardoso observed. Thus, the research challenge is to “try to classify triple-negative disease as something positive” and then target that biomarker.

Recently, there has been some success in this arena, she observed.

A biomarker has been identified in triple-negative breast cancer, and it has been successfully targeted by a novel drug, sacituzumab govitecan, an antibody–drug conjugate that targets the human trophoblast cell-surface antigen 2 (Trop-2). The drug was granted accelerated approval in the United States in April 2020 based on response data, but has since confirmed clinical benefit in a trial that showed an improvement in overall survival of about 5 months (compared with physician’s choice of chemotherapy) in metastatic triple-negative disease.  

Approached for comment, Harold Burstein, MD, PhD, of Dana-Farber Cancer Institute in Boston, Massachusetts, told Medscape Medical News in an email: “There have been tremendous strides in treatment options for each of the three major clinical types of advanced breast cancers — HER2+, ER+, and triple-negative, in recent years.”

“Studies reported within the past 1-2 years have identified drugs in each of these treatment areas that improve overall survival and extend the range of options for women living with metastatic cancer,” he said.

“New classes of drugs such as immune checkpoint inhibitors and PARP inhibitors are now in clinical use, and are powerful agents in patients with certain kinds of breast cancer defined by biomarkers. All this progress bodes well for continuing to see improvement in outcomes for women with advanced breast cancer,” he said.

Cardoso and Burstein have reported no relevant financial relationships.

Advanced Breast Cancer Sixth International Consensus Conference (ABC 6). Held virtually November 2-4, 2021.

Nick Mulcahy is an award-winning senior journalist for Medscape, focusing on oncology, and can be reached at [email protected] and on Twitter: @MulcahyNick

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