Advances in lymphoma diagnostics and therapy (Proceedings)
The last few years have brought some interesting and novel discoveries with regard to the diagnosis and therapy of lymphoma in pets. These will be discussed in detail in the following hour.
Pcr for antigen receptor rearrangement
Determining whether a lymphoma originates from a T cell or B cell (also called determining the immunophenotype) is one of the most important pieces of information that can be supplied to a client to assist in prognostication. Most pathology labs are capable of determining immunophenotype by means of immunohistochemistry on tissue sections. Another method for establishing immunophenotype is through PCR for antigen receptor rearrangmenent (PARR). This molecular diagnostic test evaluates the presence or absence of a clonally expanded population of B cells or T cells, and is approximately 85% sensitive and 95% specific for canine lymphoid neoplasia. It can also be performed on feline samples, although the sensitivity and specificity are not as great. An advantage of this technique is that it can be performed on almost any type of sample, including air-dried or previously stained cytology slides, effusions, aspirates, cerebrospinal fluid, and peripheral blood. Formalin-fixed tissues cannot be used.Flow cytometry
The University of California at Davis, Colorado State University and North Carolina State University can perform immunophenoptying on fresh fine-needle aspirates or peripheral blood samples using flow cytometry. This technique allows the labeling of individual cells with antibodies to determine the origin of a lymphoma or leukemia. This has been useful as a diagnostic for the patient with leukocytosis, helping to distinguish between likely reactive leukocytosis and leukemia. It may also be able to provide prognostic information in patients with lymphoid leukemias. Finally, it appears to be useful for distinguishing lymphoma from thymoma in animals with mediastinal masses. The participating labs typically accept samples from around the USA. Fresh cells are required, and fine-needle aspirates must be placed in special transport medium and shipped overnight for evaluation.
The forms for flow cytometry and PCR at Colorado State University can be downloaded from: http://www.dlab.colostate.edu/webdocs/services/index.htm
Maintenance vs. No maintenance
One of the debates among veterinary oncologists centers around the utility of "extended maintenance" chemotherapy for pets with LSA. In human medicine, treatment is rarely continued for longer than 6 to 10 months, and randomized trials have not demonstrated significant survival advantage for patients receiving extended maintenance chemotherapy. However, the dosages of chemotherapeutic agents that dogs with LSA can tolerate are less than half of what a human would receive of the same agents. We previously investigated the effect of discontinuing treatment after 25 weeks of standard-dose chemotherapy. Analysis of a cohort of 50 dogs treated with this protocol showed no statistical difference in survival time or disease-free interval when compared with dogs receiving a similar protocol including extended maintenance chemotherapy. There are no studies in the literature investigating the necessity for maintenance chemotherapy in feline LSA. In the Author's practice, this knowledge gap is discussed with owners and a choice is provided between discontinuation after 6 months of treatment and continued maintenance chemotherapy.
Asparaginase vs. No asparaginase
Older publications routinely include a single injection of asparaginase at the beginning of multi-agent treatment. Recently, 2 studies have demonstrated no improvement in any measure of outcome in dogs receiving asparaginase. For this reason, the author chooses to omit asparaginase from initial treatment and save it for use as a potential therapy at relapse.
Oral vs. Intravenous cyclophosphamide
Although all of the statistics generated regarding the efficacy of multi-agent lymphoma chemotherapy protocols such as the UW-Madison protocol have utilized injectable cyclophosphamide, many clinicians substitute oral cyclophosphamide at the same dose. It is not clear whether this is as efficacious, owing to cyclophosphamide's unknown oral bioavailability in dogs. Investigators at CSU have recently performed a pharmacokinetic analysis comparing oral versus injectable cyclophosphamide in dogs with lymphoma, and preliminary results indicate that, while there is a significant difference in concentrations of the parent drug, the active metabolite of cyclophosphamide is quite similar between the 2 routes of administration, suggesting probable equal efficacy. One remaining advantage to injectable cyclophosphamide is that the appropriate dose can be administered with greater exactness that can be attained with tablets.
Is there an all-oral chemotherapy protocol that is effective for canine lymphoma?
Many owners may be uncomfortable with the idea of injectable chemotherapy but may be more comfortable with the concept of oral chemotherapy pills. While owner education regarding the excellent tolerability of most injectable chemotherapy, and the potential for side effects even with oral medications, may help to change some owners' minds, there remains a subset of owners for whom an oral chemotherapy protocol is the only acceptable choice.
Oral chemotherapy can be efficacious for 2 very specific forms of lymphoma: the low-grade, lymphocytic gastrointestinal lymphomas in cats (prednisone and chlorambucil), and cutaneous T cell lymphomas in dogs (lomustine ± prednisone). However, for the majority of intermediate- or high-grade multicentric lymphomas in dogs or multicentric/mediastinal/ intestinal lymphomas in cats, no efficacious oral protocol as been identified. One recent study evaluated the efficacy of prednisone and lomustine as first-line therapy for canine multicentric lymphoma and found it to be no better than what has been reported with prednisone alone.