Lapatinib Increases Overall Survival in Metastatic Breast Cancer Patients With HER2-Positive Circulating Tumor Cells

Findings published in the special "Cancer: Biology & Diagnostics" issue of ADLM's Clinical Chemistry journal

WASHINGTON, Jan. 4, 2024 /PRNewswire/ -- A new study shows that lapatinib, a drug used for the treatment of metastatic HER2-positive cancer, is associated with improved overall survival in patients with initially HER2-negative metastatic breast cancer and HER2-positive circulating tumor cells (CTCs). This groundbreaking finding was published today in a special issue of the Association for Diagnostics & Laboratory Medicine's (formerly AACC's) Clinical Chemistry journal titled "Cancer: Biology & Diagnostics."

View the full study here: https://doi.org/10.1093/clinchem/hvad144

About 10%-20% of all breast cancer tumors express elevated levels of a protein called HER2, which causes cells to divide uncontrollably. These HER2-positive tumors respond well to HER2-targeted therapy. However, the invasive tissue biopsies needed to measure HER2 expression levels in metastatic lesions — which can differ from levels in primary tumors — are not always feasible due to the location of the metastatic site, making it difficult to comprehensively determine HER2 status. Testing the HER2 status of CTCs, which only requires a blood sample, is a promising alternative to invasive biopsy for identifying patients with metastatic cancer who might benefit from HER2-targeted therapy.

In order to assess the feasibility of this approach, the DETECT III trial sought to evaluate the efficacy of HER2-targeted lapatinib therapy for metastatic breast cancer based on a diagnosis of HER2-positive CTCs at the time of metastatic relapse. It is the largest randomized trial to ever address this question. Patients eligible for the trial had metastatic breast cancer not treatable by surgery or radiotherapy alone, as well as HER2-negative tumors and/or lesions and HER2-positive CTCs. Patients received either standard therapy (chemotherapy or endocrine therapy) or standard therapy with lapatinib, and rates of CTC clearance were assessed at various intervals during the trial.

No significant differences were found in CTC clearance rates between the standard and lapatinib arms, regardless of CTCs' positivity levels and when clearance rates were measured. Patients in the lapatinib arm also showed a modest yet insignificant improvement in progression free survival rates compared to those in the standard arm. Yet remarkably, patients receiving lapatinib had a median survival time of 20.5 months, more than twice as long as patients who underwent standard therapy. The lapatinib-induced boost in overall survivability was observed throughout the length of DETECT III, which spanned over five years.

The study authors speculate that lapatinib may target a specific but small subgroup of CTCs with high tumor-initiating capacity, which would account for low levels of overall CTC clearance alongside large improvements in overall survivability.

"DETECT III is the first clinical study indicating that phenotyping of CTCs might have clinical utility for stratification of [metastatic breast] cancer patients to HER2-targeting therapies," the authors wrote. "CTC-guided therapy may be useful to optimize treatment strategies and should be further investigated in randomized clinical trials."

About the Association for Diagnostics & Laboratory Medicine (ADLM)

Dedicated to achieving better health through laboratory medicine, ADLM (formerly AACC) brings together more than 70,000 clinical laboratory professionals, physicians, research scientists, and business leaders from around the world focused on clinical chemistry, molecular diagnostics, mass spectrometry, translational medicine, lab management, and other areas of progressing laboratory science. Since 1948, ADLM has worked to advance the common interests of the field, providing programs that advance scientific collaboration, knowledge, expertise, and innovation. For more information, visit www.myadlm.org.

Clinical Chemistry (clinchem.org) is the leading international journal of laboratory medicine, featuring nearly 400 peer-reviewed studies every year that help patients get accurate diagnoses and essential care. This vital research is advancing areas of healthcare ranging from genetic testing and drug monitoring to pediatrics and appropriate test utilization.

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SOURCE Association for Diagnostics & Laboratory Medicine (ADLM)