LOUISVILLE, Ky. -- Dogs are being diagnosed with cancer like never before and they're dying at a rate that baffles veterinarians and overwhelms pet owners, WLKY-TV reported.

Chemotherapy is not something most pet owners think their dogs will ever experience, but, then again, most never think their dogs will get cancer.

Tamyra Spear's dog, Gracie, has lymphosarcoma, a cancer of the blood, and so does Debbie Clayton's dog, Floyd.

"If she weren't treated, she would die in about six weeks," said Spear. "That's the news I got."

It's one of the most common forms of canine cancer.

"If someone could tell me exactly what to do to prevent this so it would never happen again, I would do every single thing," said Clayton.

"Many of my clients ask me that, and it's the same answer as in humans -- we're not sure of all the underlying factors," said Dr. Catherine Daley.

Daley, an oncologist with Metropolitan Veterinary Specialists, said that her office treated hundreds of dogs with cancer with cancer this year.

WLKY spoke by phone with Dr. Demian Dressler, a vet who started DogCancerBlog.com when he realized cancer had become the canine world's No. 1 killer.

"It's horrible when you think about the reality of what's going on," said Dressler.

He said environmental factors such as herbicides and pesticides on lawns and gardens could be to blame.

Smoking around your animal is also on his list.

Clayton didn't think about those factors.

"For the first few years that I had him, I did smoke in my house. And when I had my daughter, I stopped smoking in my house, which, right there, what does that tell you I was thinking?" she said.

Dressler also said pet owners need to pay closer attention to what they're feeding their pets. Stay away from carbs and sugars, she said.

Dressler warned that preservatives in pet foods can be carcinogenic. As with humans, fresh foods are better than processed, and when it comes to natural proteins such as chicken or beef, Dressler said to make sure it's the first ingredient on the pet food you buy.

Daley said there could be something else behind the cancer increase.

"I don't think it's more prevalent than in the past," she said. "I think people are more willing to seek help when they get a diagnosis of cancer."

When dogs get chemotherapy, they typically don't get debilitating side-effects seen in people because dogs get much lower doses.

The goal for dogs with cancer is not a cure; it's improving quality of life until the cancer takes over.

Gracie has lost weight since her last chemo treatment, and after a 15-month battle that included a remission, Spear thinks Gracie's time has come.

"We never really expected to go through chemo and all of this, but really it's been a really good experience," Spear said. "For 15 months, she's had a wonderful life and we've gotten to enjoy her for those 15 months."