Menarini Silicon Biosystems announces PACE trial biomarker analysis results confirming clinical utility of CELLSEARCH® CTC enumeration to guide treatment decisions in a specific metastatic breast cancer subtype

The secondary analysis of the PACE trial highlights the value of counting Circulating Tumor Cells (CTCs) in the blood to help guide treatment escalation or de-escalation in patients with hormone receptor-positive (HR+), HER2-negative (HER2-) metastatic breast cancer whose disease progressed after treatment with aromatase inhibitors plus CDK4/6 inhibitors. CTC count is a standalone predictive biomarker, independent of clinical risk factors and circulating tumor DNA.

BOLOGNA, Italy and HUNTINGDON VALLEY, Pa., Dec. 22, 2025 /PRNewswire/ -- Menarini Silicon Biosystems, a pioneer of cell-based liquid biopsy technology, announced today the publication in Clinical Cancer Research^[1] of the CTC biomarker analysis from the PACE trial, a multicenter phase II clinical study initiated in 2017. The analysis examined whether CTC count could provide prognostic and predictive information in HR+/HER2- metastatic breast cancer patients progressing after first-line treatment. 

203 patients were randomized to receive either endocrine monotherapy or combination therapy consisting of a doublet (endocrine therapy plus a CDK4/6 inhibitor) or a triplet regimen (endocrine therapy plus a CDK4/6 inhibitor and an immune checkpoint inhibitor). Based on their CTC level, patients were classified into two prognostic groups: those with less than 5 CTCs per 7.5 mL of blood, defined as having indolent disease, and those with 5 or more CTCs, defined as having aggressive disease. While no significant difference in progression-free survival was observed between treatment groups in the overall population, patients with aggressive disease (5 or more CTCs) experienced a meaningful reduction in the risk of progression when treated with combination therapies. More specifically, the risk of progression was reduced by 57% in patients receiving doublet therapy and 74% in patients receiving triplet therapy, when compared with endocrine monotherapy.

Lorenzo Gerratana, MD, Associate Professor at the University of Udine and Physician Scientist at IRCCS CRO Aviano (Italy) and first author of the PACE biomarker analysis, said: "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. 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". As the biological mechanisms driving resistance to CDK4/6 inhibitors are still not fully understood, there is a clear unmet need for reliable biomarkers to guide treatment decisions following disease progression.

These recent findings are consistent with the results of the STIC trial^[2], published in 2024, which showed that treatment decisions guided by CTC counts could differ from physician choice and, when discordant, either led to improved survival outcomes or allowed treatment de-escalation without negatively affecting survival.

"The STIC and PACE trials consistently demonstrate how our CELLSEARCH CTC enumeration can improve patient management in the heterogeneous metastatic breast cancer setting, where both resistance mechanisms and disease progression remain a challenge," said Fabio Piazzalunga, President of Menarini Silicon Biosystems (MSB). "This test is available for In Vitro Diagnostic Use in Europe and China, and in the U.S. through our CAP/CLIA/ISO 15189 accredited laboratory in Huntingdon Valley, Pa., USA. We are committed to supporting physicians to make more informed decisions, whether to intensify treatment to control disease progression or reduce treatment intensity to preserve quality of life".

About CELLSEARCH

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.

CELLSEARCH CTC Kit is not cleared or approved for use to guide specific treatment decisions.  The clinical data described herein involve an investigational use of the CELLSEARCH system outside its cleared indications, and have not been submitted to or reviewed by any regulatory authority for approval.

For more information on the full intended use and limitations of the CELLSEARCH system, please refer to the Instructions for Use at http://documents.cellsearchctc.com/.

About MSB

Menarini Silicon Biosystems, based in Bologna, Italy, and Huntingdon Valley, Pa., U.S., is a wholly owned subsidiary of the Menarini Group, a multinational pharmaceutical, biotechnology, and diagnostics company headquartered in Florence, Italy, with more than 17,000 employees in 140 countries.

^[1] https://pubmed.ncbi.nlm.nih.gov/40853871/
^[2] https://pubmed.ncbi.nlm.nih.gov/37931185/ 

Contact: PAVY Consulting, Linda PAVY, lipavy@pavyconsulting.com 

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