Medina, a 20-year-old female sloth bear, died Wednesday, Dec 29, during a health examination intended to evaluate symptoms of lethargy and decreased appetite observed by zookeepers.

“When keepers noticed a sudden, drastic decrease in the bear’s activity, we immediately scheduled a health examination in order to gain more knowledge about the cause of her symptoms and provide the best care possible for Medina,” said Martin Ramirez, Woodland Park Zoo mammal curator in a press release.

Shortly after being immobilized for the examination, the bear’s heart stopped and could not be revived.

The postmortem examination revealed extensive carcinoma of the liver that had spread to nearby tissues.

“The cancer we discovered in this bear is known to be a leading cause of death in older aged sloth bears,” according to Dr. Darin Collins, the zoo’s director of Animal Health, “and likely severely compromised her health when she was immobilized under anesthesia.”

Medina arrived at Woodland Park Zoo in 2008 and her partner Randy, a 14-year-old male sloth bear, remains on exhibit at the zoo.

“We’re truly saddened by the loss of Medina,” said Ramirez. “She was a feisty bear, one who always made her presence known, and she will be greatly missed by zoo staff and our visitors who come to be inspired by and connect with such amazing animals.”

Sloth bears—native to Bangladesh, Bhutan, India, Nepal and Sri Lanka—are an endangered species. Fewer than 10,000 remain in the wild. Their survival is challenged by fragmented populations, deforestation and the bear parts trade. While their life span in the wild is unknown, sloth bears have been known to live up to 40 years in captivity.