Introduction: Thymidine kinase is an established marker of cancer cell proliferation and its activity can be measured in blood. We and others have recently shown that baseline and dynamic evaluation of circulating thymidine kinase activity (TKa) during treatment gives prognostic and predictive information in patients with HR+, HER2-negative metastatic BC treated with endocrine therapy alone, as well as in the setting of CDK4/6 inhibition. However, there is limited data regarding the role of TKa as a prognostic biomarker in operable BC. Here we present a retrospective analysis of TKa in serum samples collected in a cohort of premenopausal women with operable BC enrolled in a phase III adjuvant multicenter clinical trial (NCT00201851).

Materials and methods: Serum samples were available for 644 (87%) of participants prospectively enrolled in a randomized trial between 2003 and 2009 in South East Asia. All women were premenopausal, had stage II-IIIB HR+ operable BC and uniformly received bilateral surgical oophorectomy concurrent with mastectomy followed by tamoxifen alone for five years. Patients did not receive chemotherapy or targeted therapy pre- or post-operatively. Participants were randomized in the study according to the timing of surgery with respect to the phase of the menstrual cycle. Serum samples were collected preoperatively on the day of surgery. Serum TKa was measured using the ELISA-based DiviTum™ assay (Biovica, Sweden). TKa analysis was performed at a central laboratory, blind to clinical data. Baseline TKa values were correlated with clinico-pathological characteristics and clinical outcome. Clinical outcome was estimated using the Kaplan-Meier method.

Results: The majority of patients had both estrogen and progesterone receptor positive tumors (94% and 92% respectively), 65% were HER2 negative (18% positive; 17% unknown). Most had pT2 or pT3 disease (60% and 27% respectively), and more than half were node-positive (pN0 42%, pN1 27%, pN2 19%, pN3 11%, pNx 1%). The overall median TKa value was 65.4 Du/L. At five years, patients with a baseline TKa value below the median had a disease-free survival (DFS) rate of 75% versus 61% in those with a baseline over the median (HR 1.82, 95% CI 1.37-2.4, p<0.001). Similar results were observed when women with HER2+ disease were excluded from analysis (HR 1.71, 95% CI 1.21-2.42, p=0.0025). Further prognostic precision was achieved when TKa values were divided by quartiles, with a 5 year DFS rate of 81%, 69%, 63% and 58% observed in the 1st, 2nd, 3rd and 4th quartiles respectively. After adjusting for major prognostic factors and randomization arm, TKa remained an independent marker.

Conclusions: This study shows pre-operative TKa measured in serum is a strong prognostic marker in a large cohort of women with HR+ operable BC uniformly treated within a clinical trial. The notable rate of recurrence seen within this cohort of patients derived from non-high income countries may be mainly attributed to the relative degree of disease burden at diagnosis. TKa may be seen as a potential circulating marker of proliferation akin to tumor Ki67, which may provide useful prognostic information to guide adjuvant therapies.

Citation Format: Luca Malorni, Ilenia Migliaccio, Chiara Biagioni, Lorenzo Rossi, Irene De Santo, Richard L Love, Amelia McCartney, Mattias Bergqvist, Martina Bonechi, Francesca De Luca, Francesca Galardi, Matteo Benelli, Dario Romagnoli, Emanuela Risi, Laura Biganzoli, Adriano Laudico, Nguyen Van Dinh, Angelo Di Leo. Serum thymidine kinase-1 activity (TKa) as a prognostic marker in premenopausal women with hormone receptor positive (HR+) operable breast cancer (BC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-06-11.