By J. Lee Talbott, DVM DACVIM (Medical Oncology)
The diagnosis of cancer in veterinary patients is made based on the pet’s medical history, clinical signs, physical exam, and diagnostic tests including (but not limited to) blood work, radiographs, ultrasound, specialized molecular tests when indicated, and in some cases advanced imaging (computed tomography or magnetic resonance imaging – CT/MRI). With the diagnosis of cancer increasing in our veterinary patients and advances in veterinary diagnostic capabilities, there is a recognized need for early detection of cancer in our patients, prior to the development of clinical signs. This is where the development and utility of screening tests becomes important.
The goal of any screening test is to provide early detection of a disease in order to provide faster and more successful treatment. The role of early detection isn’t without controversy including the risk to benefit ratio for patients and whether or not there is a survival benefit associated with early detection.1,2 An appropriate screening test is any test that has acceptable specificity (i.e. few false positive results) and isn’t used as a stand-alone test. As a general rule, most screening tests are designed to quantitate the presence of “biomarkers” – measurable indicators of particular biological states or conditions that are used to detect, screen, diagnose, and monitor disease.
This article is meant to provide basic information on some available cancer screening/detection tests and their use for cancer diagnosis (however this is not an exhaustive list). It is the author’s opinion that when used appropriately, these may be useful adjunctive tests, however cancer screening tests remain in their infancy. It is important to understand that randomized controlled clinical trials and continued research are necessary to fully ascertain how best to utilize and interpret these tests. At this time the author doesn’t recommend the use of a single screening test utilizing a biomarker for the diagnosis of cancer.
Tests Available in Veterinary Medicine
Thymidine Kinase (TK)
Thymidine Kinase is an enzyme involved in DNA synthesis. It is present in two forms, TK1 (located within the cytosol) and TK2 (located within the mitochondria). TK1 is associated with cell proliferation and can be measured in the serum with high levels of expression because the enzyme leaks out of the cell membrane.1 TK1 expression is limited to cells with rapid proliferation rates, notably hematopoietic malignancies.1,3 Conversely solid tumors in dogs and humans do not show consistently increased levels of serumTK1, precluding their use as a biomarker in human and veterinary oncology.3
Veterinary Diagnostics Institute (VDI; Simi Valley, CA, USA) has recently marketed VDI-TKcanine+, a canine blood test for the diagnostic, prognostic, and therapeutic monitoring for dogs with lymphoma and hemangiosarcoma.1 In veterinary species, high levels of serum TK1 (compared with normal range) are detected in canine and feline lymphoma, as well as splenic hemangiosarcoma.3-5 It is important to understand that other conditions, including inflammation and viral infections can increase the activity of serum TK1. VDI-TKcanine+ is advertised as a dual biomarker panel for dogs with suspected or confirmed cancer, by combining C-reactive protein (cCRP), an accepted marker for inflammation with TK1.3 According to data on their website, VDI-TKcanine+ has a sensitivity of 96% and a specificity of 85% for the diagnosis of cancer (i.e there is a moderate to high number of false negatives).
Additionally VDI offers a blood test to aid in differentiation of feline inflammatory bowel disease and gastrointestinal lymphoma. While a technical data sheet is available on the VDI website, no peer-reviewed studies have been published at this time.6
Thymidine Kinase 1 (TK1)
The use of TK1 has been defined as a biomarker for canine hemangiosarcoma.4 In one study, the serum TK1 levels were higher in dogs with diagnosed hemangiosarcoma as compared with normal controls.4 In this particular study the use of TK1 was not found to be able to differentiate between benign and malignant lesions.
Veterinary Bladder Tumor Antigen (VBTA)
This test allows for the qualitative detection of tumor analytes in canine urine by using antibodies against a bladder tumor-associated glycoprotein complex. While the sensitivity of this test is between 85-90%, the specificity is 41-86%, and multiple factors (glucosuria, proteinuria, hematuria, and pyuria) contribute to the high and variable number of false positives.7 The specificity of this test is much less when patients are demonstrating signs of urinary tract disease. The best use of this test should be for the diagnosis of urinary bladder TCC in asymptomatic patients, specifically predisposed breeds (i.e. Scottish Terriers and Beagles) –figure 1. Positive results should be interpreted in light of other diagnostic tests results, and the VBTA test should not be used alone to diagnose or initiate treatment of TCC.
Canine Cancer Detection BRAF (CADET BRAF) and BRAF – PLUS
Figure 1: Scottish Terrier dogs are 18 times more likely to develop TCC as compared with any other breed.
The Canine Cancer Detection BRAF Mutation Detection Assay is a DNA-based approach to screen dogs for evidence of urinary bladder transitional cell carcinoma (TCC) or urothelial TCC.9 This test evaluates free-catch urine samples for the presence of the BRAF mutation and is manufactured by Sentinel Biomedical, a comparative health company lead by a team of scientists based out of Raleigh, NC. According to one study, a single mutation in the BRAF gene is identified in 85% of confirmed cases of canine TCC and urothelial carcinoma (UC) and is not affected by bacteriuria or hematuria.8 Please note that one of the authors of this study is one of the researchers within Sentinel Biomedical. The presence of the BRAF mutation in urine is specific for the presence of TCC/UC, however what remains to be determined is whether early intervention and treatment will result in a survival benefit. Additionally, the type of early intervention and treatment (surgery, radiation, chemotherapy, or some combination of these) is not well defined and is likely to vary based on additional diagnostic results (ultrasound, CT, biopsy, etc). The company also reports that the CADET BRAF test can be used for monitoring patients with TCC/UC during treatment to determine response and relapse.8 Because this test remains in its infancy there are no standardized recommendations for treatment when the mutation is identified and this is at the clinician’s discretion. While this test is noninvasive, has a rapid turnaround time (2-3 days), and is relatively inexpensive, the test requires a large volume of urine (40-60mls) collected within 2-3 days.
Sentinel Biomedical recently marketed BRAF-PLUS. This is an add-on test (using the same urine sample sent in for BRAF analysis) to detect TCC/UC in dogs that present with clinical signs consistent with TCC but do not harbor the BRAF mutation. While it is difficult to ascertain what the test is evaluating (based on the information on the company website), they claim that the addition of BRAF-PLUS detects more than 2/3rds of those TCC/UC cases not identified by BRAF alone (15%), improving the test sensitivity to greater than 95%.9
The need for cancer screening tests in human and veterinary medicine is imperative for early detection and intervention, ultimately translating to longer survival times and even curative intent treatments. This is an active area of ongoing research with undeniable potential, however it is important to remember that screening tests are meant to be used and interpreted in conjunction with conventional diagnostic methods. For those cases where the above mentioned tests are indicated, it is the author’s recommendation to use these tests under the direction and instruction of an oncologist. Additionally, it may be necessary to communicate with the scientists within the manufacturing company in order to aid in case-based result interpretation.
- Cancer Screening Tests for Small Animals. Vet Clin Small Anim 44 (2014)871-881
- Modiano JK, Sharkey LC. A practical guide to diagnostic testing for veterinary cancer patients. 2012.
- Selting KA, Sharp CR, Ringold R, et al. Serum thymidine kinase1 and C-reactive protein as biomarkers for screening clinically healthy dogs for occult disease. Vet Comp Oncol 2013.
- Thamm DH, Kamstock DA, Sharp CR, et al. Elevated serum thymidine kinase activity in canine splenic hemangiosarcoma. Vet Comp Oncol 2011; 10(4):292-302.
- Elliot JW, Cripps P, Blackwood L. Thymidine kinase assay in canine lymphoma. Vet Comp Oncolo 2011; 11(1):1-13
- Veterinary Diagnostics Institute. VDI-TKfeline. In: Veterinary Diagnostics Institute technical data sheet. 2011.
- Henry CJ, Tyler JW, McEntee MC, et al. Evaluation of a bladder tumor antigen test
as a screening test for transitional cell carcinoma of the lower urinary tract in
Am J Vet Res 2003;64(8):1017–20.
- Mochizuki H, Shapiro SG, Breen M. Detection of BRAF Mutation in Urine DNA as a Molectular Diagnostic for Canine Urothelial and Prostatic Carcinoma. PLoS ONE 10(12): e0144170. https://doi.org/10.1371/journal.pone.0144170
- Sentinelbiomedical.com, www.sentinelbiomedical.com/