Abstract Title

Institution

Patient Population

Key Findings

"Interrogating serum thymidine kinase activity with CDK4/6 inhibitor-based therapies: real-world experience in the metastatic and adjuvant setting."

Roswell Park, US

HR+ MBC 1ST LINE HR+ ADJUVANT BC ABEMA

TKa is predictive in adjuvant BC

• An on therapy TKa level of <50 DuA is predictive for a >20 month response to therapy in CDK4/6i treated pts diagnosed with HR+ MBC
• An on-therapy TKa level of >243 is predictive for <8 months of response to therapy
• Adjuvant BC pts treated with abemaciclib had a highly significant reduction in TKa between BL and C1/C2
• Elevated TKa levels were observed with disease recurrence

"Evaluation of proliferation biomarker serum thymidine kinase activity and prediction of early relapse in HR-positive HER2 negative high-risk early breast cancer: Analysis from the PENELOPE-B trial."

The German Breast Cancer Group, Germany, and US

HR+ ADJUVANT BC PALBO

TKa is prognostic in adjuvant BC
• In PENELOPE-B, BL TKa values >250 DuA were prognostic for early relapse within the 1st year of adjuvant therapy
• CPS-EG scores, in contrast, were not prognostic.
• Pts with early disease relapse also had an increase in TKa levels at the time of recurrence.

"ctDNA and serum thymidine kinase activity as tools to stratify ER+/HER2- metastatic breast cancer patients treated with endocrine therapy and CDK4/6 inhibitors: preliminary results of the TIRESIAS trial."

Hospital of Prato, Italy

HR+ MBC 1ST LINE

TKa offers an attractive alternative to ctDNA

• Circulating tumor DNA (ctDNA) and thymidine kinase activity (TKa) give complimentary information
• TKa and ctDNA dynamic changes are concordant
• TKa offers a cost-effective and easier alternative to ctDNA for non-invasive monitoring of early response to therapy

"Thymidine kinase activity as a prognostic biomarker for first-line CDK4/6 inhibitor efficacy in the Personalised Disease Monitoring in Metastatic Breast Cancer (PDM-MBC) Study."

Jönköping Hospital Sweden, Christie in Manchester, UK

HR+ MBC 1ST LINE

TKa levels are prognostic for CDK4/6i efficacy in HR+ MBC

• Baseline (BL) TKa >250 DuA associated with shorter PFS (13.5 mo vs not reached) and OS (30.3 vs 51.8 mo) in 1st line CDK4/6 inhibitor pts
• A TKa value >100 DuA at any cycle 1 timepoint (BL, D15, D28) predicted for a significantly worse PFS and OS vs staying below 100 DuA at all 3 timepoints.

"The Role of Serum Thymidine Kinase 1 (TK1) as a Prognostic Factor in Luminal HER2 Negative Breast Cancer."

IRBLeida, Spain

HR+ Early breast cancer pre/post surgery
HR+ MBC 1ST LINE

TKa is a prognostic biomarker in luminal BC

• EBC pts with high TKa also have a high OncotypeDx score.
• MBC pts who had an on-therapy increase in TKa had progression in 3-6 mo
• MBC pts who had an on-therapy decrease in TKa had a response lasting greater than 3-6 mo

"Thymidine kinase activity as a prognostic and predictive biomarker in the Phase II PACE trial of CDK4/6 inhibition beyond progression ."

Dana Farber Cancer Institute, US

HR+ MBC 2ND LINE - PALBO

TKa can predict 2nd line CDK4/6i benefit

• There currently is no existing biomarker to predict the benefit to a CDK4/6i following progression on a previous CDK4/6i
• High C2D1 on-treatment TKa (>250 DuA) was associated with a lack of response to palbociclib beyond progression on a prior CDK4/6i
• Authors conclude TKa could facilitate clinical decisions in this context

"Thymidine kinase activity as a predictive biomarker for benefit to a second line CDK4/6 inhibitor: analysis from the MAINTAIN trial.

Emory, US

HR+ MBC 2ND LINE RIBO

TKa can predict 2nd line CDK4/6i benefit

• TKa levels on C2D1 significantly predicted for the benefit to ribociclib after progression on a prior CDK4/6i
• TKa <250 DuA had a PFS of 10.9 mo on ribociclib
• TKa >250 DuA had a PFS of 2.7 mo on ribociclib