# Pilot Study of a Novel First-Line Protocol (THOP) for Intermediate–Large B-Cell Lymphoma in Dogs

## TL;DR

A new 15-week chemotherapy protocol called THOP was tested in dogs with B-cell lymphoma and showed promising results in terms of effectiveness and tolerability.

## Contribution

A novel cyclophosphamide-free chemotherapy protocol (THOP) was developed and evaluated as a first-line treatment for B-cell lymphoma in dogs.

## Key findings

- All 14 dogs achieved complete remission with a median time to progression of 269 days.
- THOP was well tolerated with minimal severe side effects reported.
- The protocol shows potential for further study as an alternative to the standard CHOP protocol.

## Abstract

B-cell lymphoma is one of the most common cancer diagnoses in pet dogs. Currently, the standard treatment is a 19- or 25-week chemotherapy protocol consisting of four chemotherapy drugs: doxorubicin, cyclophosphamide, vincristine, and prednisone, or CHOP. CHOP is very effective, but half of dogs do not finish the treatment because the lymphoma relapses, the timing of which has been associated with cyclophosphamide. The goal of this prospective clinical trial was to identify side effects and early indication of effectiveness of a protocol that replaces cyclophosphamide with a different chemotherapy drug, temozolomide, to create a new protocol, THOP, that is only 15 weeks long. Fourteen pet dogs with B-cell lymphoma were treated with THOP as their first chemotherapy protocol. All dogs finished the treatment in complete remission. The results indicate that the protocol is well tolerated and may have similar effectiveness to the current standard of care. These data will be helpful in designing a larger prospective clinical trial that directly compares THOP with CHOP effectiveness.

The current standard of care for treatment of intermediate–large B-cell lymphoma in dogs is a CHOP-based chemotherapy protocol. On-protocol disease progression is reported to be temporally associated with cyclophosphamide administration. The objectives of this prospective pilot clinical trial were to describe the adverse event profile and identify early signal of efficacy of a novel cyclophosphamide-free chemotherapy protocol consisting of temozolomide, doxorubicin, vincristine, and prednisone (THOP) as first-line treatment in dogs with diffuse large cell B-cell lymphoma. Treatment-naïve dogs with intermediate–large B-cell lymphoma were enrolled. THOP was administered as a three-week cycle for five cycles. Fourteen dogs were enrolled. All dogs achieved complete remission with a median time to progression (TTP) of 269 days and a median survival of 433 days. There were five grade III and four grade IV hematologic toxicities reported; one grade III gastrointestinal toxicity was observed. THOP appears to be well tolerated and an effective first-line protocol for the treatment of intermediate–large B-cell lymphoma in dogs.