Lymphoma is a major nasal cancer in cats, comprising ≤65% of nasal cancer cases.^1-3 Cancer-specific treatment options include radiation (local treatment), chemotherapy (systemic treatment), or a combination of both.^4-6 It is unclear whether local, systemic, or combined treatment should be used as a first-line approach for localized lymphoma in cats or whether chemotherapy should be reserved for certain disease stages or recurrences.^4-6 Furthermore, the rate and location of tumor progression after treatment with radiation alone have not been well-defined.

This multi-institutional retrospective study evaluated cats with presumed localized sinonasal lymphoma treated with radiation alone using 1 of 3 protocols. The objective was to describe the failure pattern, time to progression, and overall survival rate and to identify prognostic factors that predict outcome.

Fifty-one cats were included in the study; the most common clinical signs were nasal discharge (74.5%) and stertor/stridor (70.6%). Fifty-one percent of cats had advanced tumors (clinical stage III; orbital, nasopharyngeal, subcutaneous, or submucosal involvement). Tumor grade was available in 42 cats; 40 (95.2%) had a high-grade tumor. These data collectively suggest that lymphoma is an aggressive cancer in cats.

Clinical response to treatment was subjectively assessed (ie, improvement in nasal signs) in 50 cats; responses were characterized as complete in 40 cats (80%), partial in 8 cats (16%), and stable in 2 cats (4%). Objective assessment of tumor response based on imaging was difficult to assess, as there were no standardized timepoints. In the 50 cats in which clinical response to treatment was assessed, disease progression occurred in 49% in the following pattern: 9.8% local progression (sinonasal, nasopharynx, or both), 3.9% locoregional (regional lymph node involvement only), 5.9% local and locoregional, 17.6% systemic (extending to distant organs), and 11.8% local and systemic. Despite the lengthy overall median time to progression (ie, 32.4 months), when systemic progression occurred, it developed early (ie, within 1.5-7 months after radiation) in all but 2 cats.

Radiation protocol and other factors evaluated, including glucocorticoid use and tumor factors (eg, size, grade, location, stage), were not predictive of overall time to progression or overall survival time.

This study demonstrates that radiation is an effective treatment for localized sinonasal lymphoma with a long time to progression; however, in 33% of the cats, systemic disease progression occurred soon after radiation.

Key pearls to put into practice:

Because the most common clinical signs in this study were nasal discharge and stertor/stridor, nasal lymphoma should be high on the differential list for cats presented with chronic and/or recurrent nasal signs.

Most cats were diagnosed with advanced-stage and high-grade phenotype; however, many experienced long-term benefits from radiation treatment.

One-third of cats experienced early systemic progression. Full staging was not required in this study; however, full staging is recommended for clinical cases so the best treatment protocol can be planned. If there is clear evidence of systemic disease, combination therapy (ie, radiation and chemotherapy) may be beneficial.