Do pre-treatment biopsy characteristics predict early tumor progression in feline nasal diffuse large B-cell lymphoma treated with radiotherapy

The standard of care treatment for localised feline nasal lymphoma (FeNL) is radiation therapy (RT). Early local or systemicfailure occurs in 17%–45% of cats treated with RT with or without chemotherapy. The aim of this study was to determine if pre-treatment biopsy characteristics could predict early tumour progression in FeNL. Inclusion criteria consisted of histologicallyconfirmed FeNL, available paraffin blocks of diagnostic quality, localised to the sinonasal cavity on staging pre-RT, treated withIMRT/IGRT (10 × 4.2 Gy) without chemotherapy and at least 1 year follow-up. All pre-RT biopsies were reviewed and evaluatedwith CD3, CD20, CD79a, pan- CK and Ki- 67 immunohistochemistry and the mitotic activity index was determined. The primaryendpoint was progression-free survival (PFS) at 1 year and hazard-ratios (HR) with confidence interval (CI) were calculated.Twenty-eight cats fit the inclusion criteria, and all had diffuse large B-cell lymphoma. Seventeen cats (61%) were progression freeat 1 year. Of the 11 cats that progressed in the first year, two had local progression, two had both local and systemic progressionand seven had systemic progression. The mitotic index (HR: 1.03, CI 0.9–1.19, p = 0.645), Ki- 67 (HR: 1.00, CI 0.98–1.02, p = 0.845)and > 30% of tumour-infiltrating T cells (HR: 0.38, CI 0.09–1.56, p = 0.175) were not significantly associated with PFS. In this uni-formly RT treated population of FeNL, none of the evaluated pre-RT histologic parameters could predict early treatment failure.