But measuring progress remains difficult. Her cancer does not show up radiographically which makes it nearly impossible with the methods available to tell if the drugs are working. Chatfield said the team will basically monitor Peanut’s behavior for signs of remission.

“On the one hand, we are really lucky we caught it, but the bad part about it is it’s so small that it’s hard to detect or monitor,’’ said Chatfield, also Jungle Island’s general curator, said. “But it’s such a hyper-aggressive, invasive cancer, we had to do treatment. Otherwise, she would not survive.”

The staff is careful not to say the “C-word” in Peanut’s presence, not because she understands the language but because she does understand behavior.

“When people talk about cancer, they can’t help but be foreboding and their mood shifts,’’ Chatfield said. “She is very perceptive, so we are just trying to have a positive outlook around here.’’

After each treatment, Peanut returns to her enclosure, a wide space with hammocks. But because she is usually very tired, she is isolated for a few days. Her sister, Pumpkin, knows something is amiss.

“She walks up to her and makes Peanut stretch out her arms so she can see where the hair has been shaved for treatment,’’ Jacobs said. “Then she gets real close to Peanut’s face to see her eyes, as if to say, ‘what’s wrong?’ ’’

So far, the only other change has been in her taste buds: she no longer cares for baked sweet potatoes, once a favorite.

The cancer was discovered almost by chance in May.

“Normally she is an attention getter. She liked to paint and take bubble baths. She likes to eat blueberry and jackfruit,’’ Jacobs said. But in the spring, she said, she noticed a change. “She just wasn’t herself. She didn’t have much energy, took a lot of naps and seemed tired all the time.’’

Tissue samples and an ultrasound found Peanut had irregular bowels, the result of an intestinal blockage. After the operation in late May, Chatfield had a sample sent to a California lab where the initial cancer diagnosis was made, though Peanut had no growth, mass or lesions.

The news was shocking to Jungle Island’s team because this cancer is typically found in late stages in great apes 30 to 40 years old — or during an autopsy. The University of Miami confirmed the diagnosis.

Dr. Offiong Ikpatt, a UM hematopathologist, did more specialized molecular testing. He immediately knew it was cancer.

“It looked exactly the same. If I wasn’t told, I would have thought I was looking at human tissue,’’ Ikpatt said.

Born in captivity, Peanut and Pumpkin came to Jungle Island as babies and have been cared for by Jacobs from the beginning. The orangutans quickly developed distinct personalities: Peanut is friendly, curious and feisty. Pumpkin is a thinker, the quieter of the two, more inclined to while away the days atop her enclosure.

On a recent visit, not long after her final treatment, Peanut sat on the ground, almost in Jacobs’ lap, playing with her xylophone. She snacked on handfuls of baby carrots and peanuts, meticulously shelling the nuts with her lower lip. “Peanut knows something is wrong, but she is getting through this like a champion,’’ Jacobs said tearfully. “She still has the most incredible sparkle in her eyes.’’