CHICAGO – Progress in breast cancer treatment over the past 2 decades has reduced expected mortality from both early-stage and metastatic disease, according to a new model that looked at 10-year distant recurrence-free survival and survival time after metastatic diagnosis, among other factors.
“There has been an accelerating influx of new treatments for breast cancer starting around 1990. We wished to ask whether and to what extent decades of metastatic treatment advances may have affected population level breast cancer mortality,” said Jennifer Lee Caswell-Jin, MD, during a presentation of the study at the annual meeting of the American Society of Clinical Oncology.
“Our models find that metastatic treatments improved population-level survival in all breast cancer subtypes since 2000 with substantial variability by subtype," said Dr. Caswell-Jin, who is a medical oncologist with Stanford (Calif.) Medicine specializing in breast cancer.
The study is based on an analysis of four models from the Cancer Intervention and Surveillance Modeling Network (CISNET). The models simulated breast cancer mortality between 2000 and 2019 factoring in the use of mammography, efficacy and dissemination of estrogen receptor (ER) and HER2-specific treatments of early-stage (stages I-III) and metastatic (stage IV or distant recurrence) disease, but also non–cancer-related mortality. The models compared overall and ER/HER2-specific breast cancer mortality rates during this period with estimated rates with no screening or treatment, and then attributed mortality reductions to screening, early-stage, or metastatic treatment.
The results were compared with three clinical trials that tested therapies in different subtypes of metastatic disease. Dr. Caswell-Jin and colleagues adjusted the analysis to reflect expected differences between clinical trial populations and the broader population by sampling simulated patients who resembled the trial population.
The investigators found that, at 71%, the biggest drop in mortality rates were for women with ER+/HER2+ breast cancer, followed by 61% for women with ER-/HER2+ breast cancer and 59% for women with ER+/HER2– breast cancer. Triple-negative breast cancer – one of the most challenging breast cancers to treat – only saw a drop of 40% during this period. About 19% of the overall reduction in breast cancer mortality were caused by treatments after metastasis.
The median survival after a diagnosis of ER+/HER2– metastatic recurrence increased from 2 years in 2000 to 3.5 years in 2019. In triple-negative breast cancer, the increase was more modest, from 1.2 years in 2000 to 1.8 years in 2019. After a diagnosis of metastatic recurrence of ER+/HER2+ breast cancer, median survival increased from 2.3 years in 2000 to 4.8 years in 2019, and for ER–/HER2+ breast cancer, from 2.2 years in 2000 to 3.9 years in 2019.
“How much metastatic treatments contributed to the overall mortality reduction varied over time depending on what therapies were entering the metastatic setting at that time and what therapies were transitioning from the metastatic to early-stage setting,” Dr. Caswell-Jin said.
The study did not include sacituzumab govitecan for metastatic triple-negative breast cancer, or trastuzumab deruxtecan and tucatinib for HER2-positive disease, which were approved after 2020. “The numbers that we cite will be better today for triple-negative breast cancer because of those two drugs. And will be even better for HER2-positive breast cancer because of those two drugs,” she said.
During the Q&A portion of the presentation, Daniel Hayes, MD, the Stuart B. Padnos Professor of Breast Cancer Research at the University of Michigan Rogel Cancer Center, Ann Arbor, asked about the potential of CISNET as an in-practice diagnostic tool.
“We’ve traditionally told patients who have metastatic disease that they will not be cured. I told two patients that on Tuesday. Can CISNET modeling let us begin to see if there is indeed now, with the improved therapies we have, a group of patients who do appear to be cured, or is that not possible?” he asked.
Perhaps, Dr. Caswell-Jin said, in a very small population of older patients with HER2-positive breast cancer that did in fact occur, but to a very small degree.