Medical Mystery Surrounds 7 Boston-Area Sisters Diagnosed With Breast Cancer

A Boston-area family is at the center of a medical mystery after one sister was recently diagnosed with breast cancer, making her the seventh sister in the family to have the disease.

Making the story of the Belmont sisters even more complex is that some of the sisters have also had the disease more than once.

Betty Belmont Harmon, the oldest of the sisters, was the first to be diagnosed, back in 1995. Over the next 20 years, each sister was diagnosed, one after the other.

The sisters -- Betty Belmont Harmon, Mary Belmont Perdios, Winnie Belmont, Irene Belmont Quigley, Nancy Belmont, Dottie Belmont Loring and Judy Belmont Counterman -- told ABC News’ Linzie Janis they had thoughts over those two decades of “Who’s next” and “How come it’s taking so long for me to get it?”

The sisters say they used to joke that the one sister to keep escaping the disease, Nancy Belmont, must be adopted. That is until last April, when Nancy was diagnosed with Stage 4 breast cancer.

“When Nancy got it, I passed out,” said Mary Belmont Perdios. “Hers was the worst. Stage 4."

"We were crushed," she added. "Every one of us were in tears.”

There is no strong family history of disease in the sisters’ family, and their doctors say most are negative for the BRCA breast cancer genes. The sisters’ two other siblings – two brothers - are both deceased but neither of them died of cancer-related causes.

Some of the sisters said they wonder whether the coal plant they grew up next to in South Boston caused the cancer, recalling childhood memories of dust brushing on their bed sheets while they were hanging outside to dry.

“It was bad,” said the youngest sister, Judy Counterman. Dr. Irene Kuter, an oncologist at Massachusetts General Hospital, has treated six of the seven sisters.

"I haven't seen as many individuals in one family like this," Kuter said. "They're a fighting family." While an environmental or genetic link to the sisters’ breast cancer is still possible, Kuter says she is exploring another theory.

“Maybe it’s something unusual,” Dr. Kuter said. “Maybe it’s a virus.”

If it turned out a virus sparked the sisters’ cancer, it means there is a chance the sisters could end up teaching the world something new about breast cancer.