What's on the horizon for lymphoma? (Proceedings)

This talk will cover a general review of lymphoma then discuss various novel therapies currently available for the palliation and control of this cancer in dogs. Lymphoma is one of the most common forms of cancer in dogs, cats, and humans. Lymphoma in dogs most closely resembles non-Hodgkin's lymphoma in people, and similar to its counterpart in people, canine lymphoma is difficult if not impossible to cure. Cats will develop lymphoma with a different anatomic distribution (often gastrointestinal) and in some cases, can develop a Hodgkin's-like lymphoma that is very responsive to therapy. As systemic disease by nature, lymphoma is treated primarily by systemic chemotherapy. Many efforts over the past 30 years have failed to significantly improve outcome compared to CHOP-based chemotherapy (CHOP represents the 4 mainstay chemotherapy drugs used in lymphoma treatment: cyclophosphamide, doxorubicin (hydroxydaunorubicin), vincristine (Oncovin), and prednisone). However, new therapies hold promise for the future. Our efforts include not only new agents, but attempts to improve upon past successes by refining currently available techniques.

Staging

Because this disease travels by lymphatics, staging tests typically follow the flow of lymph around the body. Again, since this is a systemic disease by nature, the word "metastatic" is rarely applied, rather advanced stage of disease may be considered. After peripheral lymph node evaluation, hemolymphatic organs such as spleen and liver are assessed for involvement. If viscera are involved, a minimum of stage 4 is assigned. While confirmation of diagnosis by lymph node cytology and/or biopsy is necessary, and bloodwork crucial to assess liver and kidney function (for metabolism of chemotherapy drugs, especially liver function is important for the drugs used in this disease) as well as bone marrow function prior to myelosuppressive therapy, other staging tests are more controversial.

Imaging (radiographs and/or ultrasound) are noninvasive and can provide additional information about stage of disease and how a patient might best be monitored. For example, a dog may have sublumbar lymphadenopathy in addition to the peripheral node involvement. Without imaging and/or rectal examination (part of a thorough routine physical examination), this may be underappreciated. The dog could relapse in the sublumbar nodes before peripheral node enlargement and the clinician would not know to monitor for this without appropriately staging at presentation.

Bone marrow aspiration is part of complete clinical staging and true clinical stage cannot be accurately assigned without a bone marrow aspirate. Although most dogs will demonstrate abnormalities on complete blood count in the face of bone marrow involvement, a small percentage (around 10-15%) can have relatively normal CBC with some evidence of bone marrow involvement. Furthermore, the definition of a positive bone marrow is poorly defined. Therefore, the necessity of this test is questioned, especially in the face of a normal CBC. A recent study on stage migration did not show a difference in assessment of stage 4 vs. stage 5 when evaluating various staging methods and the effect of stage migration (shifting of stage assignement in a given patient as a result of improved or changed methods of detecting disease such as advent of improved imaging methods).

Prognostic factors

Widely accepted prognostic factors include substage (sick or hypercalcemic is bad), immunophenotype (T-cell origin is bad), and prior treatment with prednisone (poor prognostic factor). Smaller dogs tend to have greater toxicity from chemotherapy but fare better with treatment.

Diagnostic advances (see also cancer testing: beyond the biopsy)

Petscreen

Petscreen, Inc. (www.pet-screen.com), is a proteomics-based company out of the United Kingdom focused on novel biomarkers for a variety of disease conditions. Studies by the company found 19 serum protein peaks that are significantly different between dogs with (n=87) or without (n=92) lymphoma, 2 of which are attractive candidate markers and are currently being sequenced. This test can serve to confirm a suspected or elusive diagnosis, and may be useful in monitoring response to therapy. Studies are underway to clarify the role of this test in monitoring patients. This company also offers a chemosensitivity assay that uses a novel methodology compared to previously reported assays

PARR

Polymerase chain reaction for Antigen Receptor gene Rearrangement (PARR) for canine lymphoma has been developed at Colorado State University by Dr. Anne Avery. This test is based on the fact that the immune system produces a highly diverse set of antigen receptors in order to respond to as many antigens as possible. When clonal expansion of a lymphocyte occurs, as is the case when cancer develops from one renegade cell, the resulting population tends to produce only one type of receptor. This cell population can be amplified using PCR and the monotony of receptors is detected as a single band on a gel, whereas inflammatory conditions or normal lymphocytes produce a ladder effect. The test is available through Colorado State at www.dlab.colostate.edu. This test, as with the Petscreen test, can be used to confirm an elusive lymphoma diagnosis.

Flow cytometry

Immunophenotyping has traditionally been done on formalin-fixed biopsy samples using immunohistochemical markers. However, antibodies for this process can also be applied to cells in suspension, allowing immunophenotyping to be done on fine needle aspirate samples. This is convenient for dogs with lymphoma as it does not involve anesthesia and provides prognostic information with T-cell performing worse than B-cell for multicentric lymphoma. This service is available through many laboratories including Idexx, Veterinary Diagnostics (www.vdxpathology.com), UC Davis, North Carolina State University, and Colorado State University.

Thymidine kinase

Unlike the proliferation indices discussed above, thymidine kinase is a soluble biomarker of proliferation which means it can be measured in the bloodstream. This enzyme is part of the salvage pathway for DNA synthesis and can reflect a population of cells in the body that is proliferating and preliminary studies have shown great promise in cancers such as B-cell lymphoma and hemangiosarcoma. TK will most likely be used to confirm a diagnosis, assess the aggressiveness of a cancer as well as monitor response to treatment. Studies are in progress and the test will be commercially available by the time of the meeting. For more information, check the website at www.vetdiag.com or visit their booth at CVC.

Standard treatment options

Chemotherapy is the mainstay of treatment for lymphoma in dogs. As mentioned above, CHOP-based chemotherapy prevails. L-asparaginase is often used at induction of remission and has been shown to improve remission rates, however overall survival is not convincingly improved. A few studies have evaluated the value of L-asparaginase in a multidrug protocol, and found no improvement in outcome, but unfortunately those studies only evaluated subcutaneous l-asparaginase which was shown in a separate study to be inferior to intramuscular delivery. Therefore the question of how important it is to include l-asparaginase in the initial chemotherapy treatment is not fully answered. CHOP protocols have used various sequences of the same drugs, and modifications include different sequences, and different dose intensities as well as accelerated and pulsed protocols, all with similar outcome. Overall median survival times are around 12-18 months.

Rescue chemotherapy typically is less effective (30-50% remission rates) and less durable (approximately half the first remission time) than frontline chemotherapy. Drugs that are popular in the rescue setting include CCNU, mitoxantrone, and mechlorethamine-oncovin (vincristine)-procarbazine-prednisone (MOPP) protocols, among others. Currently at the University of Missouri we are evaluating combination cytosine arabinoside with carboplatin and mitoxantrone in the rescue setting.

Novel treatment options

Following the concept of xenogeneic cancer therapy for immune system augmentation, a clinical trial ongoing at the Animal Medical Center in New York City, and through Brightheart Veterinary, is evaluating the use of anti-CD20 therapy for B cell lymphoma. Antibodies against CD20 have had a significant impact on B cell lymphoma therapy in people.

Among the more exciting new options for dogs with lymphoma is the availability of bone marrow transplantation at North Carolina State University. Dr. Steve Suter and his team have created a clinical service dedicated to autologous bone marrow transplantation for dogs with lymphoma. Advantages include the opportunity for increased cure rates, and disadvantages include the risk of sepsis during engraftment, long waiting list, and cost (approximately $15,000). Dogs must be in a solid clinical remission at the time of transplantation. Results are pending as the service has not been available for long, but transplants have already been successful.