DENVER (AP/CBS4) – An elderly lion at the Denver Zoo has died while being treated for cancer.

Zookeepers noticed in March that the lion named Rian had grown lethargic. Tests found a large mass in his abdomen and he was euthanized on Wednesday.

The lion was undergoing an experimental treatment based on therapy typically used for domestic cats suffering from lymphoma.

Veterinarians were hoping to gather valuable information about how chemotherapy could help other zoo lions and large cats.

The Denver Zoo shared more details about Rian on their Facebook page:

Denver Zoo is deeply saddened to announce the passing of “Rian,” a 15-year-old male South African lion. Rian had recently been undergoing chemotherapy treatment for an aggressive cancer originating in his spleen. Veterinarians had hoped the treatment would extend and improve his quality of life while providing valuable information about how chemotherapy could help other zoo lions and large cats. Unfortunately, on the morning of Wednesday, June 19, zookeepers noticed that his quality of life had decreased to the point that they decided to humanely euthanize him.

“This decision was very difficult. Rian has been a treasured member of the Denver Zoo family for so long and we were hoping for a recovery,” says Denver Zoo Curator of Large Mammals Hollie Colahan. “When Rian began treatment we were encouraged as he was improving – showing more energy and his appetite improved. Unfortunately, he took a turn for the worse over the last two days and we didn’t want him to suffer. We will miss him dearly.”

Rian’s treatment began in mid-March after zookeepers noticed he had been acting significantly lethargic, prompting closer examination. Exploratory surgery revealed his spleen had grown to weigh 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 and that, even after the spleen was removed, the cancer had migrated from the spleen to other parts of Rian’s body.

Collaborating with specialists with Colorado State University, zookeepers and veterinarians elected to start chemotherapy, alternating between intravenous and oral treatments, something that has never been performed on a lion before. This was meant to not only improve Rian’s quality of life, but provide valuable information about how chemotherapy could help other large cats in zoos. Rian received his first treatment of chemotherapy on May 27 and repeated it every week. Initially, zookeepers and veterinarians were encouraged by his early results, but in the last couple days it became evident his quality of life was quickly diminishing and zookeepers and vets decided it was time to say goodbye.

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 their arrival later that year. 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.

LINK: Denver Zoo

(TM and © Copyright 2013 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2013 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)


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