Thymidine kinase 1 in mBC treatment response

Thymidine kinase 1 (TK1) is one of the key predictive biomarkers in metastatic breast cancer (mBC) that shows prognosis and responsiveness to therapy. TK1 activity levels correspond with the course of the illness and the effectiveness of cancer treatment¹, providing information on the dynamics of the disease and the effectiveness of therapy. This information is then used by clinicians and medical professionals to guide therapeutic choices and improve mBC patient management.

Combined with other screening methods, TK1 biomarker testing is a non-invasive method of diagnosing and monitoring cancers like breast cancer, lymphoma, and leukemia².

TK1 biomarker testing – the process

Thymidine kinase is a blood-based biomarker that needs to be evaluated in a laboratory using a blood specimen. Using the approved sample bottles and a standardized procedure, a blood sample is obtained and brought to the lab for examination.

While TKa testing can provide valuable information in some instances, it is not a standalone monitoring tool. TK testing can be added to the Imaging (CT-/PET-Scan) schedule and should always be considered in relation to the diagnostic results and clinical assessments for a more accurate interpretation of results. The patient’s medical history, symptoms, and other diagnostic tests should be considered when interpreting TK results and making clinical decisions.

TK activity levels can be monitored over time to assess the effectiveness of cancer treatment. Since TK diffuses from proliferating tumor cells to the bloodstream, serum TK activity measurements have shown changes in levels during progression and treatment of HR+ metastatic breast cancer and other cancers, such as lung, bladder, and colorectal cancer Specifically, in patients with metastatic breast cancer, a decrease in TK activity may indicate a positive response to therapy, while persistently elevated activities may suggest treatment resistance or disease progression³.

The turnaround time for this assay is quick, making it a preferred way for cancer monitoring. Usually, the lab results are obtained within 24 hours of sample collection. A novel means of assaying TK1 enzyme activity, chemiluminescence assay, promises a quicker turnaround time of less than 24 hours⁴. This hopes to put TK1 levels assay at the forefront of solid cancer disease management.

TK testing has drawbacks, which includes the likelihood of false positives or negatives and the variation in testing techniques. Numerous studies have found different sensitivity activities, but the specifics have yet to be determined.

Methods for TK1 biomarker testing

Various methods are available for TK1 testing, which include enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), and polymerase chain reaction (PCR). Each method has advantages and limitations, which practitioners should know when interpreting test results.

Elevated TK1 activities in cancers led to the development of clinical measurement assays. Early methods, like anion exchange chromatography, had limitations in sample processing and solvent use. The [3H]-deoxythymidine phosphorylation assay, which uses radioactivity, improved efficiency by reducing reagent use and increasing sample throughout².

The DiviTum® TKa assay by Biovica® is a non-radiometric method that measures bromodeoxyuridine or 5-bromo-2′-deoxyuridine (BrdU) incorporation into DNA. Initially, BrdU is phosphorylated to monophosphate form (BrdUMP) by TK in samples, then to triphosphate form (BrdUTP) by yeast kinases. BrdUTP is captured by PolyA strands on a microtiter plate well and detected with an anti-BrdUTP monoclonal antibody conjugated to alkaline phosphatase. The resulting color, proportional to TK activity, is measured at 405 nm. TK activity, expressed in DiviTum units/L (Du/L), is determined from a calibration curve using TK1 standards. This assay measures total TK activity⁵.

Correlating thymidine kinase 1 (TK1) activities with metastatic breast cancer (mBC) treatment response offers valuable insights into therapeutic efficacy. A notable trend emerges – decreased TK1 activities often show positive responses to various treatment modalities, which include chemotherapy, endocrine therapy, and targeted therapies.

Baseline thymidine kinase is measured before breast cancer therapy begins to serve as a benchmark for tracking the impact of the prescribed medicine. Following the start of treatment, follow-up TK1 testing is done. In a patient with mBC undergoing chemotherapy, regular TK1 measurements reveal a steady decline, which aligns with tumor regression and improved clinical outcomes. Conversely, persistent elevation or an abrupt increase in TK1 activities signal treatment resistance or disease progression⁶.

Early identification of resistance through TK1 assessment is paramount in guiding clinical decisions. Clinicians can pre-emptively modify treatment regimens by detecting TK1 activities before conventional imaging methods manifest alterations, optimizing patient care. Moreover, TK1 is a prognostic indicator, which aids in predicting treatment outcomes and overall survival rates in mBC patients⁷.

A case study8 was reported on breast cancer patients and colorectal cancer patients at the outpatient clinic of the oncology department of Cerrahpasa Medical Faculty, Istanbul. All patients underwent comprehensive evaluations, including history-taking, physical examinations, and laboratory tests.

Clinicopathological features were assessed in breast cancer patients, including histology, menopausal status, hormone receptor status, lymph node involvement, tumor grade, size, and staging. Adjuvant chemotherapy comprised epirubicin, cyclophosphamide, and 5-fluorouracil. Similarly, colorectal cancer patients underwent staging and received oxaliplatin, folic acid, and 5-fluorouracil as adjuvant chemotherapy.

Clinical parameters, including TK1 activities, were measured twice: before chemotherapy initiation and after six cycles. Samples were stored at -80°C until analysis.

Serum TK1 activity was assessed intermittently using an enzyme-linked immunosorbent assay (ELISA) kit. The assay quantified TK1 activity via bromo-deoxyuridine phosphorylation, according to the manufacturer’s instructions.

The result revealed that the mean TK1 activity was significantly elevated in breast and colorectal cancer compared to controls. After six chemotherapy cycles, TK1 activity decreased from baseline in both cancers. The cutoff point for TK1 was >44.36 Du/L, with 68.29% sensitivity and 100% specificity. In conclusion, pre-treatment TK1 activity is a valuable marker for evaluating the progress in the treatment of breast cancer and colorectal cancer⁸.

The results of management for patients with metastatic breast cancer (mBC) can potentially be enhanced by integrating TK1 (thymidine kinase 1) testing into clinical procedures. There are several ways to accomplish this. Through blood tests that measure TK1 levels, physicians can identify cancer recurrences sooner than they can with traditional imaging techniques⁹. This makes early intervention possible and may lead to more successful treatment plans.

Oncologists may decide to adopt more aggressive treatment regimens or targeted medicines if high TK1 levels indicate a more aggressive tumor phenotype. On the other hand, low TK1 levels can point to a tumor that is less aggressive or responds well to conventional therapies¹⁰. Treatment-related toxicity may be decreased, and results may be enhanced with this individualized approach to treatment planning.

Serum TK1 levels can also be used as a biomarker to gauge how well a treatment works. Patients with continuously elevated TK1 levels may not respond to medication or may even be resistant to it. Oncologists can prevent lengthy or inefficient therapy that might result in needless side effects without offering therapeutic benefits by detecting non-responders early with TK1 testing¹¹.

After starting treatment, if TK1 levels don’t decrease, doctors might consider further choices based on each patient’s tumor biology and molecular profile. This strategy reduces the possibility of subjecting patients to ineffective therapies.

Lastly, testing for TK1 can reveal important information about how aggressive a malignancy is and how it responds to therapy¹⁰. Clinicians can then more effectively customize treatment regimens depending on the unique characteristics of each patient by assessing TK1 levels, which might help prevent the overtreatment of individuals with less aggressive illnesses.

TK1 levels can be used as biomarkers to track the effectiveness of a treatment over time. With this real-time evaluation, doctors may quickly modify treatment plans by increasing therapy or de-escalating it if the malignancy shows an excellent response to treatment, reducing needless side effects of treatment and maintaining quality of life.

Testing for TK1 sheds light on the growth of tumors and how they react to therapy. Combined with other screening and monitoring methods, TK1 biomarker testing can aid in cancer treatment monitoring, helping medical professionals more accurately ascertain the ideal length of treatment for each patient, and averting situations where patients receive insufficient or excessive treatment⁷ i.e. dose optimization of therapy.

TK1 testing also makes early identification of treatment response or resistance possible¹¹. Early detection of therapeutic success or failure enables prompt modification of treatment plans. Suitable therapies can lessen the need for expensive procedures linked to severe stages of the disease and help delay the course of the illness. Clinicians can customize treatment plans based on TK1 levels to choose the most suitable for each patient. This can potentially improve treatment results and lower long-term expenditures related to ineffective therapies or disease progression.

Combined testing of TK activity alongside other tumor markers

For patients with breast cancer, frequent TK1 testing in conjunction with other indicators, including CA 15-3, CA 27.29, and Ki-67, can potentially improve individualized care and therapy optimization¹². For instance, excessive CA 15-3 and CA 27.29 levels in conjunction with high TK1 levels may suggest aggressive tumor biology and call for more aggressive treatment strategies. On the other hand, low TK1 levels combined with positive Ki-67 expression indicate a less aggressive tumor phenotype and permit therapy to be tapered down¹³.

TK levels are a valuable biomarker for evaluating the efficacy of therapy in metastatic breast cancer¹, and it certainly holds the potential to become a key blood test for breast cancer treatment monitoring. TK activity and level monitoring may help healthcare providers predict treatment resistance and prognosis earlier on in patient journeys, which can lead to potentially better treatment outcomes.

The DiviTum® TKa test is a diagnostic, prognostic, and monitoring tool designed to measure TK activity in blood samples. This produces a DiviTum activity score, which can provide valuable information regarding the disease proliferative status, particularly in mBC patients who are hormone receptor-positive and postmenopausal. Learn more about the clinical trials we have undertaken thus far, or enquire about the suitability of the test in your clinical study.

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