MOLECULAR MARKERS IN CANINE T-CELL LYMPHOMA.

The objectives of this study were to review and correlate results of the clinical, histological and immunohistochemical features of different types of canine T-cell lymphoma (CTCL) according to the World Health Organization Classification of 2002. Further, we intended to define criteria for the diagnosis of these distinct clinicopathologic entities and to determine the prevalence of molecular markers of therapeutic efficacy and thereby prognosis. Skin samples of 10 cases of cutaneous canine lymphoma were evaluated as follows: histological preparations utilizing H&E, immunohistochemistry for CD3 and CD79, and retinoid acid receptors for RAR and RXR isomers. Results of these examinations were correlated with available clinical data. The diagnoses included: mycosis fungoides (five cases), pagetoid reticulosis (three cases), and nonepitheliotropic type (two cases). All cases were CD3+CD79–, RAR+, RXR+, RXR+; nine cases were RAR+; and nine were RXR+. The presence of RAR was not detected. CD3 positivity demonstrated T-cell lineage. Differentiation of these three types of CTCL requires careful histological and cytological review as well as immunohistochemical evaluation. Clinically, nonepitheliotropic types often present with diffuse or multifocal cutaneous involvement; epitheliotropic types are less well defined and signs vary with stage of the disease. The presence of retinoid receptors suggests that, as in humans, the use of specific ligands may be effective in the treatment of canine cutaneous T-cell lymphomas. Further updating of the World Health Organization system is required to better define the characteristic features of canine CTCL to permit more accurate diagnosis and prognosis, and thus effective treatment.