CTC Measurement Blood Test Guides Treatment Decisions in Metastatic Breast Cancer Subtype

Clinicians currently lack reliable tools to determine who may benefit from intensifying therapy and who could avoid additional treatment burden. Now, blood-based analysis has shown that counting circulating tumor cells (CTCs) can independently predict disease behavior and guide more personalized treatment strategies.

Menarini Silicon Biosystems (Bologna, Italy) has reported the results of CTC biomarker analysis from the PACE trial, a multicenter, phase II clinical study initiated in 2017. Menarini’s CELLSEARCH is the only CE-marked, clinically validated, blood test cleared by the FDA for counting CTCs to aid physicians in managing patients with metastatic breast, prostate, and colorectal cancers.

The analysis examined whether CTC count could provide prognostic and predictive information in HR+/HER2- metastatic breast cancer patients progressing after first-line treatment. A total of 203 patients were randomized to endocrine monotherapy, a doublet regimen combining endocrine therapy with a CDK4/6 inhibitor, or a triplet regimen that also included an immune checkpoint inhibitor.

Patients were stratified by circulating tumor cell levels, with fewer than five cells per 7.5 mL of blood indicating indolent disease and five or more indicating aggressive disease. Although progression-free survival did not differ across treatments in the overall group, patients with aggressive disease saw a 57% reduction in progression risk with doublet therapy and a 74% reduction with triplet therapy compared with monotherapy.

The results, published in Clinical Cancer Research, suggest that CTC enumeration can act as a standalone predictive biomarker to guide treatment escalation after disease progression. Patients with indolent disease did not experience meaningful benefit from intensified therapy, indicating some individuals may safely avoid additional treatment toxicity. Researchers plan to explore further how circulating tumor cell-guided strategies can be integrated into routine clinical decision-making.

"This analysis underscores the value of CTC enumeration to identify HR+/HER2- metastatic breast cancer patients more likely to benefit from intensified therapies after disease progression on first-line treatment,” said Lorenzo Gerratana, MD, first author of the PACE biomarker analysis. “Patients with aggressive disease showed improved clinical outcomes with combination therapy, whereas patients with indolent disease did not show a meaningful benefit from treatment escalation compared to monotherapy."

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