Introduction

Alimentary lymphoma is the second most common form of lymphoma. Gastrointestinal lymphoma is generally associated with a poor prognosis and a median survival of less than eight weeks. Primary gastrointestinal lymphoma is most often of a T-cell origin.

The purpose of this retrospective study was to present a subpopulation of dogs with rectal lymphoma, which appear to have a better prognosis than the traditional alimentary lymphoma and also have a different cell origin.

Methods

Nine histologically confirmed cases of single rectal lymphoma were identified, in the period between June 1998 and May 2006, from a search of the pathology database and the clinical database of the Animal Health Trust. Full staging was performed in 8/9 dogs at the initial consultation. Survival was calculated from date of diagnosis till the date of euthanasia or the censor date (1st July 2007).

Immunohistochemistry, with B- and T-cell markers (CD79a and CD3), was performed on all original biopsies.

Results

All dogs were diagnosed with a solitary rectal mass, histologically compatible with lymphoma. Median age at time of diagnosis was 7.0 years (range 3-13.75 years).

Five of nine dogs were treated with chemotherapy, for a median follow up time of 864 days. Two of these dogs were euthanized for unrelated disease (day 117 and day 1347). Three dogs were still alive at the date of censor.

Two dogs underwent surgery; one died 6 days after surgery from wound dehiscence. The other dog received a single dose of vincristine 15 days after surgery, but further chemotherapy treatment was declined due to the experienced adverse effects. This dog was lost to follow-up 432 days after diagnosis whilst still in complete remission.

One dog did not receive any treatment and was euthanized 28 days after diagnosis. The final dog received medical supportive treatment and was euthanized 172 days after diagnosis with persistent signs of rectal discomfort.

All samples were classified as B-cell lymphomas after immunohistochemistry.

Conclusion

In this small study the prognosis for dogs with solitary rectal lymphoma, in particular those treated with chemotherapy, seems considerably better than the prognosis reported for generalised gastro-intestinal lymphoma historically.

Immunohistochemistry of these samples shows that these rectal lymphomas are more often of B-cell origin, in contrast to the expected gastro-intestinal phenotype.