Denver Zoo Lion “Rian” Begins Chemotherapy Treatment – CSU Veterinarians Partner to Help Lion with Cancer

An elderly Denver Zoo lion is undergoing cancer treatment in a manner never before attempted. Rian, a 15-year-old South African lion, underwent surgery and is receiving chemotherapy for an aggressive cancer originating in his spleen. Veterinarians hope the treatment will extend and improve his quality of life while providing valuable information about how chemotherapy could help other zoo lions and large cats.

"We are very thankful for all the help and expertise CSU doctors continue to provide. Moving forward, this will be a very valuable relationship," said Denver Zoo Staff Veterinarian Dr. Betsy Stringer.

In mid-March, zookeepers noticed Rian acting significantly lethargic, prompting zoo veterinarians to perform a full physical examination, during which tests revealed a large mass in the lion’s abdomen. Denver Zoo veterinarian Dr. Betsy Stringer then brought in Dr. Dean Hendrickson, a CSU veterinary surgeon, to perform exploratory surgery on Rian. The surgical team removed Rian’s spleen, an organ near the stomach that helps defend the body from infection. The spleen weighed almost 12 pounds – nearly 10 times its normal size. Further testing determined that Rian’s spleen grew to that size because it was infiltrated with a type of cancer known as high-grade splenic lymphoma.

Denver Zoo veterinarians regularly collaborate with CSU specialists, so oncologists at the university’s veterinary school were contacted. Dr. Douglas Thamm, a medical oncologist, recommended six months of chemotherapy. The veterinary team opted to start chemotherapy in late May in an effort to kill cancer cells that appeared to have migrated from the spleen to other parts of Rian’s body.

"This treatment approach is a first at a zoo," said Dr. Thamm. "The veterinary team working with Rian is modeling treatment on that used with domestic cats, who often suffer from lymphoma as they age."

Rian received his first treatment of chemotherapy on May 27 and repeats it every week. Though early in the process, veterinarians continue to monitor Rian’s comfort and attitude during this treatment. Overall, zookeepers and veterinarians have seen incremental improvements that suggest Rian’s quality of life is better, and that he might have a chance at recovery.

"Any time we’re doing things in wild animals there are few established treatment protocols. So we use what works in domestic animals and adapt it to the best of our knowledge," Thamm said. "Rian’s appetite has been a little better, so I hope that means he’s feeling better and the drugs are doing their job."

"We’re doing everything we can to keep Rian comfortable. We hope that this innovative treatment will help him and other lions live longer healthier lives," said Dr. Stringer.

"I hope we can establish a treatment protocol that can be tolerated by big cats and used as a jumping-off point so next time veterinarians see this they have a place to start," Thamm said.

Rian, in addition to being a beloved member of the zoo family, has lived with his brother since birth, serving as a constant companion. The lions are bachelor brothers who were born in 1998 at Knoxville Zoo in Tennessee and have lived together at Denver Zoo since they were cubs. The two are longtime favorites among zoo visitors and are known for mutually affectionate behavior in their home at the zoo’s Predator Ridge exhibit.

"We opened the zoo’s Predator Ridge exhibit in 2004 with mostly young lions, spotted hyenas and African wild dogs. Now many of them are entering their final years and are displaying natural signs of their age," says Denver Zoo Curator of Large Mammals Hollie Colahan.

The median life span of lions in zoos is 16.8 years, while lions in the wild live about 15 years. Denver Zoo is currently home to five other lions; four of these animals also are 15-years-old. They are females Natal and Baby, and males Rajah and Krueger. Sabi is a 1-year-old female cub who arrived as a gift from the Royal Family of Qatar with her two brothers on a temporary basis in late 2012; Sabi will remain at Denver Zoo for the time being.