Should we recommend spaying cats for mammary tumour prevention, and if so, at what age?

PICO Question In cats does spaying versus non-spaying reduce the risk of mammary tumours? Clinical bottom line Category of research Risk. Number and type of study designs reviewed Four studies were reviewed: three case-control studies and one retrospective cohort study. Strength of evidence Weak. Outcomes reported All four studies found a protective effect of spaying female cats against mammary tumour. One study assessed the age of spaying and found a protective effect only when spaying was performed before 1 year of age, whereas spaying after 2 years of age was associated with an increased risk of developing mammary tumour compared to intact cats. These publications contain a moderate to high risk of bias. Conclusion Based on the available evidence, spaying appears to reduce the risk of mammary tumours development in female cats. The data suggest that the protective effect is more pronounced when spaying is performed at an earlier age. However, due to the weak nature of the current evidence, further well-designed clinical trials are needed to confirm these findings and determine the optimal age for spaying.