Today's VETgirl online veterinary continuing education blog is by guest blogger Dr. Christine Mullin, VMD, Diplomate ACVIM (Oncology), who is an oncologist at Hope Veterinary Specialists. She'll be discussing what biomarkers we use in veterinary medicine in management of oncology cancer cases in dogs and cats.
Biomarkers are an emerging diagnostic trend in both human and veterinary medicine. A biomarker (short for ‘biological marker’) is an objective and quantifiable measure that characterizes a biological process. This measure is typically a molecule (e.g. a hormone or cell surface receptor) that is detectable in blood or other tissue and, in general, reflects the degree of health or disease of a patient. For example, the measure of a biomarker might indicate the activity of a metabolic pathway or expression level of a protein which might be involved in a disease process such as diabetes, pancreatitis, or cancer, to name a few. Specific uses of biomarkers in clinical medicine include risk assessment, diagnosis of disease, prognostication, monitoring of treatment response, and detection of relapse. In laboratory research, biomarkers aid in drug development, particularly by serving as surrogate endpoints for determining drug effectiveness in in vitro and in animal models. As an example, a biomarker would be a specific molecule that is associated with disease, so when that disease is effectively treated by a drug or other therapy, the level of the biomarker measurably changes. Oftentimes the changes seen within biomarkers precede clinically detectable changes, thus they can be early guides to therapy and insight into a patient’s treatment response and potential outcome.
An ideal biomarker is easily and noninvasively measured using routine lab methods, is cost efficient to run as a serial assay, is modifiable with treatment, and remains consistent amongst groups within a population. Undoubtedly, biomarkers will continue to emerge as a helpful tool within the diagnostic arsenal, particularly for diseases like cancer, but this single method of screening on its own will not and should not replace a complete physical and diagnostic examination. That being said, biomarkers may allow for early detection of tumors – a factor known to improve outcomes for cancer patients. Thus, biomarker screens could become commonplace in general practice clinics as part of a routine evaluation.
Given their burgeoning role in human medicine, biomarkers are also of interest in veterinary medicine, where they could be useful not only to enable early detection of diseases, but also to monitor the patient’s disease status during and after treatment. Much like in human medicine, biomarkers might have the biggest role in cancer medicine. In veterinary oncology, a few biomarkers have been evaluated both in vitro and in vivo, in particular for canine hemangiosarcoma (HSA), and a blood test specific to canine lymphoma (LSA) is also now commercially available.
Canine hemangiosarcoma (HSA) biomarkers
Cardiac troponin I (cTnI) has proven to be a highly specific and sensitive marker for myocardiocyte damage, and a 2010 study showed that increased cTn1 concentrations could identify cardiac HSA in dogs with pericardial effusion as well as identify cardiac involvement in dogs with HSA of other sites in the body, and both with high sensitivity and specificity. Similarly, the concentration of serum collagen XXVII peptide, a protein breakdown product involved in invasive and angiogenic processes such as HSA, was measured in the serum of dogs with HSA and levels in dogs with large metastatic burdens were found to be 9.5-fold higher than those in healthy dogs. Reductions in collagen XXVII peptide levels after surgical resection of HSA and subsequent increases with tumor recurrence demonstrate that this peptide may serve as a useful HSA biomarker. Interestingly, collagen XXVII peptide concentrations for dogs with other neoplasia (osteosarcoma, lymphoma, carcinomas) and inflammatory disease were also increased, however the values were consistently lower than those for HSA.
Another biomarker evaluated in dogs with HSA is the cytosolic enzyme thymidine kinase (TK1). This protein’s activity is closely correlated with DNA synthesis and thus is restricted to proliferating cells. A recent study demonstrated that serum TK1 activity was significantly higher in the serum of dogs with HSA compared to that of healthy dogs. However, using this marker to differentiate benign splenic masses vs. HSA was not straightforward.
TK1 has also been evaluated in other cancers, including canine and feline lymphoma, and is part of commercially available panels (“TK Canine Cancer Panel”, “TK Feline Cancer Panel”) from Veterinary Diagnostics Institute™ (www.http://vdilab.com). These panels are marketed as tools to “be used to confirm the presence of neoplastic disease when a patient presents with a suspicious mass or other indicators common with cancer.” Additionally, “[f]ollowing a diagnosis of cancer, the test is used to monitor the effectiveness of treatment and to verify remission status.” The TK Cancer Panels are composed of 2 serum biomarkers, TK1 and C-reactive protein (CRP), an acute phase protein involved in inflammatory and neoplastic responses. From these two values, the test algorithm generates a “Neoplasia index”, whose values are divided into 3 levels – negative, positive, and high positive – each one with a range. Cancer is thus highly likely for a patient with a mass or “other indicators common with cancer” and a ‘high positive’ result on the panel. However, cytology or biopsy would still necessary to make an official diagnosis.
Canine lymphoma blood test (cLBT)
Similar to the TK Canine and Feline Cancer Panels, a commercial canine lymphoma blood test (cLBT) called SENSITEST® is now available from Avacta Animal Health (http://www.avactaanimalhealth.com) and is marketed as an aid for the diagnosis of less-than-straightforward lymphoma cases (i.e. those where cytology is equivocal). The test is comprised of two biomarkers – the acute phase proteins Haptoglobin (HAPT) and C-reactive protein (CRP) - both of whose levels are increased with several disease processes including cancer. On their own, these proteins lack the specificity to diagnose lymphoma (or other cancers, for that matter), but by measuring the individual levels of these proteins and combining the readings into an algorithm, the test is reportedly able to aid in the diagnosis of lymphoma. The cLBT is reportedly able to detect relapse up to 8 weeks prior to physical signs. Thus, the cLBT is also marketed as a tool for monitoring remission during and after treatment.
In a study of 57 dogs undergoing chemotherapy for lymphoma, serial blood samples were collected over a 4 year period and the cLBT was used to monitor remission along with routine physical examination and blood work. According to the study results, the cLBT’s assessment of remission and recurrence compared well with clinicians’ assessment and was able to differentiate dogs in remission vs. those with recurring disease before the appearance of lymphadenopathy (p<0.001). Furthermore, the authors argued that the cLBT demonstrated prognostic potential since dogs with higher pre-treatment values experienced shorter survival times, while those achieving lower cLBT scores during treatment had longer survival times. The cLBT grades the remission status of each dog from 0.00 to 5.00 and from the aforementioned study of 57 dogs, statistical analysis generated thresholds for the disease status (i.e. complete remission, partial remission, progressive disease). Turnover for results of this test is reportedly 24 hours and the Avacta website indicates that for each sequential sample, Avacta will provide you with an updated graphic showing the current disease status of the dog along with the historical results. Although the company suggests that the cLBT can be used as a guide to determine remission status and whether or not additional treatment or treatment changes are indicated, particularly when the test produces a value that suggests the patient is out of remission, they also stipulate that “a discussion with a qualified oncologist would always be recommended under such circumstances”.
Clearly, these individual biomarkers and panels are promising, but not perfect tests, and should never be used in a vacuum. As in human medicine, we as a profession are still tying to figure out the best use of these assays with regard to our cancer patients. The ideal uses of these tests are still under investigation and being refined as we learn more about the biomarkers and the disease processes themselves, most of which are quite complex and cannot be fully illustrated by just one or two markers.
Alexandrakis R, Tuli SC, Ractliffe SW, et al. Utility of a multiple serum biomarker test to monitor remission status and relapse in dogs with lymphoma undergoing treatment with chemotherapy. Vet Comp Oncol Article first published online: 15 OCT 2014 | DOI: 10.1111/vco.12123.
Chun R, Kellihan HB, Henik RA, Stepien RL. Comparison of plasma cardiac troponin I concentrations among dogs with cardiac hemangiosarcoma, noncardiac hemangiosarcoma, other neoplasms, and pericardial effusion of nonhemangiosarcoma origin. J Am Vet Med Assoc 2010;237:806–811.
Kirby GM, Mackay A, Grant A, et al. Concentration of lipocalin region of collagen XXVII alpha I in the serum of dogs with hemangiosarcoma. J Vet Intern Med 2011;25:497-503.
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Thamm DH, Kamstock DA, Sharp CR, et al. Elevated serum thymidine kinase activity in canine splenic hemangiosarcoma. Vet Comp Oncol 2012;10(4):292-302.