02/03/2026
Like many teenagers with cancer, Declan Cassidy, 16, has endured having his life interrupted by surgery, chemotherapy infusions, and other treatments. In his case, however, the greatest ongoing challenge goes beyond the cancer itself.
Declan is legally blind, the result of an optic pathway glioma — a slow-growing brain tumor that forms in and around the optic nerves connecting the eye to the brain. His sight has decreased considerably since his diagnosis at age two and a half, and his care team in the Childhood Glioma Program at Dana-Farber/Boston Children’s and Blood Disorders Center has partnered with Declan and his family to contain the tumor’s growth.
But rather than lamenting what he has lost, or those things he can’t do, Declan stays busy doing all that he can — including adaptive skiing, track, and rowing, singing in a vocal ensemble, writing, creating digital art, and advocating for individuals with disabilities. A junior at the Perkins School for the Blind, he recently taped a “Day in the Life” video for a Boston-area television station in which he navigates through school halls and chemistry class with the help of his white cane and audio and tactile materials.
Even if he wanted to feel sorry for himself, Declan jokes, there wouldn’t be time.
“A lot of what people with low vision and blindness do on an everyday basis really goes unknown in the community these days, so it’s important to spread awareness,” says Declan, who has his sights set on college and then a career in graphic design or advocacy work. “Even with cancer, we can do anything if it is made accessible to us.”
The first hints that led to Declan’s 2011 cancer diagnosis came when his parents noticed their toddler holding toys close to his eyes and bumping into furniture around their home in Millis, Mass. A visit to the pediatrician revealed Declan had a profound and unexplained vision loss.
“We were referred to a neuro-ophthalmologist, who saw something suspicious on Declan’s optic nerve,” says Declan’s father, Terry. “They immediately sent us to the ER at Boston Children’s Hospital, and one day later we got an MRI and met with a neurologist.”
What they learned explained Declan’s recent behavior. An inoperable brain tumor the size of a navel orange had invaded the optic pathway system of his brain, infiltrating the nerves of his left eye. Within a week of this diagnosis, Declan and his family met their clinical team in the Childhood Brain Tumor Center at Dana-Farber/Boston Children’s.
Even at his young age, Declan made an immediate impression with his upbeat attitude as he underwent a year of weekly outpatient chemotherapy in Dana-Farber’s Jimmy Fund Clinic, which shrank the tumor considerably. Despite periods of remission and recurrence, this poise never wavered.
“Declan’s resiliency shone through in his ability to balance the rigors of chemotherapy treatments with the day-to-day of being a kid, going to school, and developing as a child into a young man, week after week, year after year, treatment after treatment,” says Mary Ann Zimmerman, CPNP, Declan’s longtime nurse practitioner. “Awe-inspiring, strong, brave, and remarkable are just a few words that come to mind when I think of Declan.”
As Declan’s vision continued to deteriorate — he is now completely blind in his left eye, with severely limited vision in his right — he transitioned from a public elementary school to The Perkins School for the Blind in fourth grade. Declan has thrived both academically and socially at Perkins’ Watertown, Mass. campus, where classes include a combination of braille, audio, and tactile learning. He has also discovered a variety of adaptive sports and honed his love for writing and art.
“My digital art is an extension of my vision,” explains Declan, who excels at landscapes and waterscapes. “Using a computer, I can zoom in and out on a drawing and incorporate the details I want. The magnifiers on my screen really break down barriers. Through adaptations like this, Perkins has given me a whole other dimension of opportunities I’d never have in public school. I’m very thankful.”
After remaining stable for close to five years, Declan’s tumor began growing again in August 2022. At this point, after three previous infusion protocols, his Dana-Farber/Boston Children’s team led by oncologist Susan N. Chi, MD, opted for a new approach. In September 2022, a tissue sample was removed from the tumor in a six-hour brain surgery known as a craniotomy. The sample was then analyzed to uncover its genetic makeup.
“The analysis revealed a very rare genetic alteration that guided treatment,” explains Chi. “This was an unexpected alteration, but one for which we had a specific medication called an oral inhibitor that could be used to target the tumor. This treatment halted further tumor growth, was well-tolerated with minimal side effects, and required infrequent clinic visits.”
Rather than missing days of school for clinic visits, Declan now just had to take a few pills each morning. Issues that once bothered him like joint and muscle pain and extreme exhaustion after infusions were virtually nonexistent on the oral inhibitor, and his dosage was lessened over time.
Chi and Zimmerman call oral inhibitors such as the one used to treat Declan’s tumor “the wave of the future” in treating many childhood brain tumors — and add that the future is now. In Declan’s case, this treatment was so effective that he is currently in the last stage of tapering off the oral inhibitor, with no regrowth of his tumor or further worsening of his vision. His clinic visits are now limited to one every three months for check-ins, lab tests, and MRIs, and he should be completely done with active treatment by early 2026.
As the end of his active treatment nears, Declan has had more time to devote to his busy life in and out of school. This includes activities with other young cancer survivors he’s met through the Jimmy Fund Clinic during the past decade.
“Declan just exudes light and joy, and if you are fortunate enough to meet him, you are impacted greatly,” says Lisa Scherber, director of Patient and Family Programs in the Jimmy Fund Clinic. “To watch him grow up into such a terrific young man is a gift. He doesn’t just live life, he attacks it.”
There is perhaps nothing Declan is more passionate about than his advocacy work. During Disability Pride Month, in July 2025, he contributed a blog entry for Perkins’ BlindNewWorld social change campaign in which he challenged people to improve accessibility every chance they get.
“I strongly believe that if we work together to break down the barriers of exclusion and make a change together, we can create an inclusive world where everyone belongs, and everyone can thrive.”
