Expression of Apoptosis-regulating Proteins Bcl-2 and Bax in Lymph Node Aspirates from Dogs with Lymphoma.

Background: Dysregulated apoptosis is a hallmark of tumorigenesis, and is also involved in resistance to cytotoxic treatment, and might be relevant in lymphoma in dogs.

Objective: That Bcl-2/Bax expression patterns differ between lymphoma immunophenotypes, and that Bcl-2/Bax ratio is correlated with prognosis.

Methods: Fifty-five client-owned dogs with multicentric lymphoma and 5 healthy dogs. Methods: Prospective, case-control study. We compared 3 methods (flow cytometry, qRT-PCR, Western blot) for Bcl-2 and Bax quantification in a subset of dogs. The effect of time on Bcl-2/Bax ratios measured by flow cytometry was assessed in lymphoma cell lines. Immunophenotype and Bcl-2/Bax expression by flow cytometry were determined in LN aspirates from all dogs with multicentric lymphoma compared to healthy dogs. Progression-free survival (PFS) was retrospectively evaluated in a group of dogs all receiving similar treatment.

Results: Bcl-2/Bax ratios remain consistent for at least 5 days after sample collection. Bcl-2/Bax ratio was higher in dogs with T-cell lymphoma (TCL; median 0.97, range 0.37-1.36) compared to B-cell lymphoma (BCL; median 0.36, range 0.07-1.45) (P < .0001) and normal dogs (median 0.36, range 0.21-0.48) (P = .0006), respectively. Dogs with Bcl-2/Bax ratios higher than the median of the group experienced a median PFS of 101 days and dogs with ratios equal and lower than the median had PFS of 130 days (P = .19).

Conclusions: Higher intrinsic resistance to apoptosis following cytotoxic treatment might contribute to the less favorable prognosis associated with multicentric TCL in dogs. Whether Bcl-2/Bax will be helpful to identify canine BCL and TCL with more aggressive and more indolent behavior, respectively, should be evaluated in larger prospective clinical studies.