Three of four members of the Welsh family of Warren Grove, just west of Charlottetown, were diagnosed with the disease last year.
"We're a normal family! And we just went upside down," Susan Welsh told CBC News.
Susan works at a grocery store, and her husband Fabian drives a taxi. Fabian and the couple's two children – 16-year-old Jenn and 21-year-old Matthew – all have the genetic flaw and have developed thyroid cancer.
"They told us that Jenn was stage one, I'm stage 3 and Matthew's stage 3," said Fabian.
Matthew is the latest to be recovering from surgery and radiation. He lost 50 pounds this spring and was close to death. The family is having difficulty accepting the disaster that has struck them.
"It's still not reality," said Jenn.
"No, it's not," her mother responded. "It still seems very surreal."
All three affected family members had surgery in the past year. There have been close to 40 trips to Halifax, and they've seen dozens of doctors. They are currently being tested every few months. With this type of cancer, there will be more tumours, and more surgeries, but they don't know when.
"When that phone rings, and it's Halifax, my heart jumps out of my mouth," said Susan.
"What now? Unknowing what's going to turn the corner for us, and that's my biggest fear."
The cancer has taken a toll on the family's health, emotions, and finances. P.E.I. is rallying around the Welshes. A benefit is planned at the Murphy Centre in Charlottetown April 25.