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 one year. Our hypothesis was that the majority of cats will be in complete remission (CR) at the end of RT and that cats in CR will have longer progression-free survival (PFS).

Methods

Single institution retrospective cohort study. Inclusion criteria were histologically 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 (CBCT). CR was defined as >90% reduction in volume. PFS was defined from first RT to systemic/local progression or death. Kaplan Meier analysis was performed and cats were divided based on end of RT response: CR versus non-CR.

Results

Thirteen cats met the inclusion criteria. By the end of RT, 7 (54%) were in CR. Overall median PFS was 660 days. The median PFS of non-CR was significantly greater (727 days) compared to CR (149 days), hazard ratio: 11 (95% CI: 2.3–51.6), (p=0.003). At 1-year post RT, 6/7 (86%) of CR had progressed versus 0/6 (0%) of non-CR. Four (30%) developed systemic LSA and 2 (15%) had local recurrence.

Conclusion

The outcome of this cohort of cats is the opposite of our expectation, suggesting that CR by the end of RT would be a negative prognostic factor. Further investigation with a larger cohort of cats is necessary to confirm this finding.