The timing couldn’t have been worse. In the middle of June 2014, Kitty Keen was ramping up preparations to show her mare Dolly Dumas in two national championship shows. The 12-year-old, flat-shod Tennessee Walking Horse mare had qualified for both The Tennessee Walking Horse Breeders’ and Exhibitors’ Association’s (TWHBEA) World Versatility Show and the Walking Horse Owners Association’s (WHOA) International Pleasure and Colt Grand Championship just a week later. But, in a grooming session a month before the first event, Kitty noticed a lump on the mare’s hindquarters. The pitch-black nodule was just to the right of her tail, about six inches below the dock. At first Keen thought it looked like a bug bite, but over several days the lump grew larger. And then it started to bleed.

Keen called in their regular veterinarian, who suspected the lesion was a skin tumor, such as a sarcoid, which might respond to freezing. But before they could follow through with the treatment, the veterinarian himself had to undergo hip surgery and was unavailable to help Dolly.

Two major shows loomed within the next week, and Keen didn’t know what to do about the bleeding lump on her mare’s hindquarter. Desperate, Keen did some research and learned that John Bennett, DVM, of Equine Services in Shelbyville, Tennessee, would be the show veterinarian at the first event. She called his office with two questions: Could Bennett help her determine exactly what this lump was? And was it serious enough to scratch Dolly from the show?

Bennett asked Keen to bring the mare to his office, and he’d try to supply some answers.

Bennett saw Dolly the next day. Overall, the mare appeared healthy, sound and fit. But after examining the lump more closely, Bennett said that he didn’t think it was a melanoma, sarcoma or other common skin tumor—those don’t tend to crack, bleed and weep as this growth was doing. Only a biopsy would provide a definitive diagnosis.

However, because Dolly was in perfect health otherwise, and the spot didn’t seem to be causing any pain or affecting her movement, Bennett said that the biopsy could wait until the show season ended in the fall. He froze the lump with liquid nitrogen and gave Keen a wound powder to encourage clotting and stop any further bleeding. He also gave her a written statement she could give to show stewards verifying the condition was not contagious and Dolly should be allowed to compete.

The lump on Dolly’s hindquarter bled during the first show, a two-day versatility event, but the wound powder kept it under control. At the second competition a week later, however, the bleeding increased and wasn’t abated by the powder.

Dolly had just won six National Championship titles in two weeks without missing a step—but it was clear that the biopsy couldn’t wait. The day after the second show ended, Keen took Dolly back to Bennett’s clinic, and the veteri-narian removed a small portion of the lump and sent it off to a pathology lab.

The news was unexpectedly awful: The lump was a hemangiosarcoma, an aggressive, malignant tumor that develops in the linings of blood vessels. The growths are most often found in the respiratory or musculoskeletal systems, but they can also appear in tissues throughout the body, including the spleen, heart, kidneys, the gastrointestinal tract, brain, sinuses and glands.

Hemangiosarcomas are rare in horses, and the finding was surprising in Dolly’s case because the tumors are typically diagnosed only after the horse is either very ill or very lame. In fact, a majority of cases are diagnosed definitively only during necropsies0.

Dolly, however, seemed absolutely fine. Bennett suggested bringing the mare back to his clinic for a more thorough examination so they could decide how to proceed. The next day, Keen watched as Bennett used an ultrasound probe to examine the tissues beneath the skin around the lump. The images on the screen showed a wide expanse of abnormal tissue extending deep into the muscles. It was clear that the lump on the skin was the just the proverbial tip of the iceberg.

Bennett recommended surgery that same day to remove the tumor. Keen agreed and headed home to wait by the phone.

Dolly was put under general anesthesia, and Bennett started his incision at the site of the lump and slowly expanded it to reveal the tumor. From the ultrasound, Bennett had guessed the growth was about the size of a softball, but as he uncovered more of it, it quickly became clear it was much larger than that.

The tumor was also complex, with “fingers” that reached deep into the surrounding muscle tissues. To reduce the risk of leaving behind any cancerous tissue, and also to limit the risk of hemorrhage, Bennett wanted to remove the tumor in a single piece, so he continued the meticulous work of tracing and exposing the entire mass while cutting it free from healthy tissue. Finally, he pulled the tumor out. It was slightly larger than a football.

How Dolly not only remained sound but competed successfully with such a large mass is baffling. The tumor had pressed against muscles deep within her hindquarters but, remarkably, hadn’t affected their function.

However, removing the tumor had left a massive wound—an almond-shaped cavity approximately a foot long and nearly as wide. It looked shocking, but suturing it closed wasn’t an option. The area was far too mobile and the skin tension would most likely rip out any stitches. And even if sutures did hold, there was a risk of extensive scarring that could permanently limit the mare’s mobility.

Instead, Bennett decided to leave the wound open and allow it to heal naturally. This would be a slow process but carried much less risk of short- or long-term complications. Dolly received painkillers, anti-inflammatory medications and antibiotics. She recovered uneventfully from anesthesia about an hour after surgery began.

Healing slowly

Keen came to visit Dolly the next morning. Bennett had prepared her for the size of the wound, but as she approached the mare from the front, all she saw was her Dolly—eating hay and looking content and normal. It wasn’t until the mare turned to walk away that she saw the gaping wound and realized Bennett hadn’t exaggerated the size of the tumor.

Two days later, the pathology report on the removed tumor confirmed that Bennett had gotten “clean margins.” In other words, he had most likely removed all of the growth and left no traces of the cancer behind to regrow. Still, hemangiosarcomas can recur after surgical removal, and there was no way of knowing whether Dolly might already have undiscovered tumors in her body. Hemangiosarcomas are notoriously hard to diagnose while the horse is alive because they can affect so many body systems.

Bennett told Keen that, because Dolly’s case was so unusual, it was impossible to predict what might happen next. The best they could do would be to monitor the wound site as well as the rest of her body and her general health. Any new lumps would need to be biopsied quickly; a blood test for serum amyloid A, a protein associated with inflammation and tumor growth, might be helpful if she became ill with no easily discernible cause.

For now, though, their most pressing concern was to keep the wound clean as it healed. Its location on the back of the hindquarter meant that gravity would help it to drain naturally, but it would have to be gently rinsed twice each day and dressed with a spray that forms a film over the wound to act as a bandage. Dolly would remain on anti-inflammatories and pain-killers for another few days and antibiotics for at least another two weeks. Bennett gave Keen detailed instructions and sent the mare home.

Each week, Kitty took a photo of the wound and emailed it to Bennett for his comments and recommendations. Slowly, the bottom of the wound filled with granulation tissue. Angry-looking, red, raw tissue was replaced with pink and then white tissue as the defect became shallower and the edges closed toward each other.

If healing had stalled or if Bennett has seen any other indications that the tumor tissue might still be present, he might have suggested chemotherapy—implanting beads impregnated with tumor-fighting chemicals into the wound site. But that step was never necessary. By fall, Keen was able to cut the cleanings back to once per day, and by winter, rinsing with water was no longer needed.

At first, Dolly was turned out in a small space near the barn with companions to help keep her quiet and settled. But the mare’s cheerful demeanor never wavered, and she remained easy to handle throughout the treatments.

Bennett gave Keen the go-ahead to start riding Dolly again in March of 2015. By then, the wound had filled in and the edges contracted so that only a thin line of scabby skin was visible.

Like horse, like owner

That spring, however, brought a new round of troubles, this time for Keen herself: She was diagnosed with cancer on her left vocal cord. After a gauntlet of tests, biopsies and consultations, her doctors determined that the best course of treatment would be radiation therapy once a day, five days a week, for six weeks.

Keen continued training Dolly throughout her treatments, even when she had to stop talking and could communicate with other people only via written notes. Her goal was to follow up on Dolly’s 2014 wins and compete in the 2015 TWHBEA World Versatility Show and the WHOA International Pleasure and Colt Grand Championship Show. By this time, the only reminder of Dolly’s ordeal was a long, hairless scar down her hindquarters.

Keen’s last radiation treatment was on a Tuesday, and two days later she started exhibiting Dolly in the TWHBEA world show, where the pair earned six more national titles. The first day of the WHOA International the following week was long and exhausting for Kitty, to the point that she had to sit out some of the classes. But despite this slower pace, they won the championships in amateur obstacle trail, adult open obstacle trail, Western riding and showmanship at halter as well as two blue ribbons in the working plantation horse competition and reserve in the overall versatility competition.

A few months later, the two cancer survivors earned three more national championships—Western riding, basic reining and adult obstacle trail—and they swept the national adult obstacle trail championships in three shows.

Looking back, Kitty says that while Dolly never seemed ill before her tumor was discovered and removed, she did have an extra spark and “brightness” during the 2015 show season. And now, two years after the mare’s lump was discovered to be much more than just a blemish, she continues to thrive, cancer-free.

This article first appeared in EQUUS issue #468, September 2016.