Nordmark, Adrian

Abstract Background: Cyclin dependent 4/6 kinase inhibitors (CDK4/6i) and endocrine therapy (ET) have improved progression-free survival (PFS) and overall survival in HR+ MBC, but progression of disease ultimately occurs. Apart from HR+ status, there are no clinically available biomarkers that enable oncologists to determine prognosis and predict response to CDK4/6i. An emerging biomarker is serum thymidine kinase 1 (TK1), a secreted marker of proliferation that is prognostic in pts with HR+ HER2- MBC. High levels of TKa are associated with inferior PFS, whereas pts with low TKa levels pretreatment, or TKa levels that decrease on ET and a CDK4/6i, have superior PFS. Notably, TKa levels rebound ≥ 5 days off Pb, with resumption of cell cycling. PROMISE (NCT0281902) is a prospective study that enrolled women with HR+ MBC starting Pb + letrozole (L) in the 1st line [FL] or Pb + fulvestrant in the 2nd line [SL] setting. The trial includes a comprehensive “omic” assessment of blood, tumor, urine and the fecal microbiome to identify novel genomic variants and pathways associated with an early decline in TKa (measured after 2 months or end of cycle [C]2) and PFS. Here, we report the association between i) pre-treatment TKa (pre-TKa) levels and PFS (i.e. from registration to the 1st disease event) and ii) TKa levels at the end of C2 (C2-TKa) and PFS-2 (i.e. from the start of C3 to the 1st disease event).Methods: TKa testing was performed using the DiviTum assay (Biovica). TKa+ disease was defined as ≥ 200 Du/L and TKa- disease as below limit of detection to 200 Du/L. Log-rank test and univariate Cox modeling were used to assess the association between pre-TKa levels and PFS and between end of C2-TKa levels and PFS-2. The database was locked on June 28, 2021. Results: Of 68 pts enrolled, 4 were ineligible and pre-TKa data was unavailable for 4. Of the remaining 60 pts (45 FL, 15 SL), the percentage of pts with pre-TKa+ disease was 33.3% in FL (15/45, 95% CI: 20.0-49.0%), and 46.7% (7/15, 95% CI: 21.4-71.9%) in the SL. The median follow-up time for pts on study was 24 months (range: 2-42 months). There were 22 disease events (13 in FL, 9 in SL). In the FL setting, PFS was significantly shorter for preTKa+ pts compared to preTKa- pts (HR: 4.15, 95% CI:1.35-12.74; p=0.007), but not for SL pts (HR: 1.11, 95% CI: 0.30-4.18, p=0.875). End of C2 TKa data was obtained for pts while on Pb (n=5), or after stopping Pb as follows: 1-4 days (n=9), 5-8 days (n=28) and 9-36 days (n=11). PFS-2 was not associated with C2-TKa in the FL (p=0.834) or SL (p=0.454) settings. An analysis of TKa levels by metastatic site will be presented at the meeting.Conclusions: A secreted biomarker of proliferation (TK1) obtained prior to initiating CDK4/6i and ET for the treatment of HR+ MBC is associated with PFS in pts receiving 1st line Pb + L, but not in those receiving 2nd line Pb + fulvestrant. While the end of C2 TKa levels were not associated with PFS, the interpretability of these data are limited, given treatment delays (0-36 days) prior to starting C3 that may result in TKa rebound. Future studies evaluating the predictive nature of TKa and Pb response should focus on earlier timepoints while on drug. Citation Format: Ciara C O'Sullivan, Jun He, Jason Sinnwell, Vera J Suman, Krishna R Kalari, Peter T Vedell, Ann M Moyer, Xiaojia Tang, Kevin J Thompson, Abe Eyman Casey, Alvaro Moreno-Aspitia, Donald W Northfelt, Minetta C Liu, Tufia C Haddad, Saranya Chumsri, Brendan McMenomy, Prema Peethambaram, Kathryn J Ruddy, Karthik V Giridhar, Roberto A Leon-Ferre, Mattias Bergqvist, Adrian Nordmark, Richard M Weinshilboum, Liewei Wang, Matthew P Goetz. Serum thymidine kinase 1 activity (TKa) levels and progression-free survival (PFS) in patients (pts) with hormone receptor positive (HR+) HER2-negative metastatic breast cancer (MBC) on palbociclib (Pb) and endocrine therapy (ET) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-13-22.

Abstract Background: Cyclin dependent 4/6 kinase inhibitors (CDK4/6i) and endocrine therapy (ET) have improved progression-free survival (PFS) and overall survival in hormone-receptor (HR)-positive metastatic breast cancer (MBC), but progression of disease is inevitable. Serum thymidine kinase-1 (TK1) is a secreted marker of proliferation that is prognostic in patients (pts) with HR-positive, HER2-negative MBC and may be predictive of ET and CDK 4/6i response. PROMISE (NCT0281902) is a prospective study enrolling women with HR-positive MBC starting palbociclib (Pb) + letrozole (L) (1st line) or Pb + fulvestrant (2nd line). We undertook a comprehensive “omic” assessment of blood, tumor, urine and the fecal microbiome in order to identify novel genomic variants and pathways associated with an early decline in TK1 (measured after 2 months) and PFS. Additionally, patient derived xenografts/organoids were generated at baseline and progression to test new therapeutic approaches to overcome resistance to CDK4/6i and ET. We report the initial association between the baseline genomic landscape and baseline TK1 levels. Methods: FFPE tumor biopsies were obtained for DNA/RNA sequencing (TempusTM) and blood samples for TK1 (Divitum® assay, Biovica) were collected pretreatment (pre-Pb) and after 2 cycles of Pb + ET (post-Pb2). Both whole-exome (exome capture) sequencing (WES) and RNA-Seq used the Integrated DNA Technologies xGen Exome Research Panel v1.0 capture kit. TK1+ disease was defined as > 200 Du/L and TK1- disease as below limit of detection up to 200 Du/L. We tested the association between genomic and transcriptomic characteristics with baseline TK1 data in pretreatment samples where both WES and RNA-seq and TK1 was available. The data were analyzed using bioinformatics pipelines for somatic and germline mutations and copy number alterations. The current analysis focuses on baseline 1st-line pre-Pb omics data in conjunction with baseline TK1 levels. The database was locked for analysis on 5/29/2020. Results: Thirty-three pts (median age: 59 yrs.) were evaluable, with paired samples for TK1 in 32. Six pts had TK1+ disease pre-Pb and post-Pb2. Twenty-two pts had TK1- disease pre-Pb and post-Pb2. Four pts had a decrease in TK1 after 2 cycles of treatment that altered the classification from TK1+ to TK1-. Both baseline RNA seq and serum TK1 (n=16) were available for 4 TK1+ and 12 TK1- pts. In this group, 476 genes were differentially regulated (398 upregulated; 78 downregulated). Pathway analysis demonstrated enrichment in complement and coagulation cascade pathway, PPAR signaling pathway, and metabolism-related pathways related to up-regulation of CYP and UGT gene families. Further testing for the association of WES data with baseline TK1+ (n=8) and TK1- (n=16) disease demonstrated somatic copy number variations on chromosomes 6, 11, 12 and 15. CDK4 copy number gains were observed in 3/8 TK1+ pts and 0/16 TK1- pts. We also observed that somatic mutations (LOH, copy number and/or SNV/INDELs) were more prevalent in the TK1+ compared to the TK1- pre-Pb group in several cancer-associated genes (FAS [p=0.06] PTEN, PIK3CB, NAB2, SOX9 and FAT1 [p=0.08], TP53, and MAP2K4 [p=0.22]). Conversely, we also noted that 6/7 pts with GATA3 mutations had TK1- disease (p=0.23). Conclusions: Using a comprehensive “omics” approach, our data suggest that a secreted biomarker of proliferation (TK1) obtained prior to initiating CDK4/6i and ET for the first line treatment of HR+ MBC is associated with established and novel genes and pathways associated with prognosis of pts receiving ET and CDK 4/6i. Analysis of on-treatment (after 2 cycles) tumor RNA seq and its association with change in TK1 as well as data from the 2nd-line cohort will be presented at the meeting. Citation Format: Ciara C O Sullivan, Krishna R Kalari, Vera J Suman, Peter T Vedell, Ann Moyer, Abraham D Eyman Casey, Jason Sinnwell, Xiaojia Tang, Kevin Thompson, Alvaro Moreno-Aspitia, Donald W Northfelt, Minetta C Liu, Tufia C Haddad, Saranya Chumsri, Prema Peethambaram, Kathryn J Ruddy, Karthik V Giridhar, Roberto A Leon-Ferre, Adrian Nordmark, Mattias Bergqvist, Brendan P McMenomy, Richard M Weinshilboum, Liewei Wang, Matthew P Goetz. Novel genomic variants and pathways associated with baseline serum thymidine kinase 1 levels in HR-positive HER2-negative MBC patients commencing palbociclib and letrozole [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-24.