"spaying a dog before her first heat cycle will decrease her chances of mammary cancer by over 98 percent."
although it is the job of the veterinarian to educate his clients and portray the pros and cons of surgery, as clients to that veterinarian, it is also our responsibility to make informed decisions and educate ourselves. Veterinarians cant make a decision for you, but they can answer questions you may have. There is a wealth of information out there. Just as you educate yourself before you purchase a new car (vs allowing the car salesman to pick the vehicle for you).
Dont base a decision on one article or study, because there are many great studies out there that look at multiple things (for instance, the UC Davis study reporting a 6% case rate of mast cell tumor in dogs that were neutered vs a 98% increase in mammary tumor rate in females spayed after their second heat cycle. In females spayed before their heat cycle, likelihood of getting mammary tumor is approx 0.05% (I couldnt find the primary article on this one, but was told this by my vet, I learned about it in my oncology course, and the link above discusses it).
thanks to everybody who shared information on this post! the UC Davis study is very interesting!