Introduction

Radiation therapy (RT) is the treatment of choice for feline sino-nasal lymphoma (fsnLSA) and the rate of local response during RT is not defined. Approximately 20–30% will develop systemic progression within 1 year. Based on our original single institution retrospective study results, our hypothesis was that cats in complete remission (CR) at the end of RT will have shorter progression-free survival (PFS).

Methods

Multi-institutional retrospective cohort study. Inclusion criteria were histologically/cytologically confirmed fsnLSA, negative stage, treated with RT only (10x4.2 Gy) and at least 1-year follow-up. Tumor volumes were measured on the first and last RT cone-beam CT/MVCT. CR was defined as >90% reduction in volume. PFS was defined from first RT to systemic/local progression or death. Kaplan/Meier analysis and Cox proportional-hazards regression was performed. Cats were divided based on end of RT response: CR versus non-CR.

Results

Forty-five cats met the inclusion criteria. By the end of RT, 13 (29%) were in CR, 30 (67%) were in non-CR, and 2 (4%) were progressive. Overall median PFS was 470 days. The median PFS of CR was significantly shorter (213 days) compared to non-CR (681 days), hazard ratio: 3.35 (95% CI: 2.1–14.2), (p=0.0007). At 18-months post RT, 12/13 (92%) of CR had progressed versus 12/30 (40%) of non-CR. Twelve (27%) developed systemic LSA, 6 (15%) had local recurrence, and 5 (11%) had both.

Conclusion

The outcome of this cohort of cats confirms our hypothesis and suggests that CR by the end of RT is a negative prognostic factor.