I recently read a good study regarding this. I will see if I can find the link tomorrow.
Also, a study from the Royal Veterinary College in the UK found out 'Due to the limited evidence available and the risk of bias in the published results, the evidence that neutering reduces the risk of mammary neoplasia, and the evidence that age at neutering has an effect, are judged to be weak and are not a sound basis for firm recommendations.”
My entire family has always had dogs and I have never heard a dog in Germany get mammary cancer. One would think that this would be the number 1 cancer in dogs there, since we dont spay or neuter, but its not.
I have also never seen a dog come to us( at my work here in Canada) with mammary cancer, but I see lymphoma and osteosarcoma 'patients' often (unfortunately).
Everybody needs to make this decision for themselves,but I hope people are open minded and do their own research before just believing whats so commonly said. The more studies appear, that can sucessfully argue this point, the more people will understand what is actually going on.