Engineer Marcos Vinícius Sampaio Vieira (in the blue shirt) with his wife and children in a photo taken last June: Five years after being treated for medullary carcinoma, molecular tests revealed that Marcos carried an inherited mutation in the RET gene. This finding led to the decision to have his young children undergo preventive surgery to completely remove their thyroids, which prevented cancer from developing in the next generation Credit: Marcos Vieira
A case report tracing 20 years of a Brazilian family's experience with hereditary medullary thyroid carcinoma shows how genetic testing shifted their care from reactive treatment to preventive surgery, sparing the next generation from developing cancer.
For the study, published in CA: A Cancer Journal for Clinicians, researchers used the case of Marcos Vinicius Sampaio Vieira, a Brazilian engineer, as the starting point for a broader review of decades of research on genetic testing for medullary thyroid carcinoma.
Vieira was 35 when a routine cardiology visit turned up thyroid nodules, one measuring 4 cm. A biopsy led to surgery, but only after his thyroid was removed was he diagnosed with medullary carcinoma, a rare, aggressive cancer with a strong genetic component.
Three years later, tests showed the cancer had metastasized to his liver. Because the disease can be inherited, doctors tested Vieira's brother, his two children and two nieces—all came back negative at first. Those results proved to be false negatives: Vieira's brother later developed visible thyroid nodules, and further testing confirmed the family carried an inherited mutation in the RET gene, identified in 1993. The mutation has nearly complete penetrance, meaning almost every carrier will develop cancer without preventive surgery.
The finding reshaped how the family approached the disease. Vieira's two children, then 7 and 10 years old, had their thyroids fully removed to prevent cancer from developing at all, as did a niece who also carried the mutation. Preserved tissue samples later showed that Vieira's father, who died of prostate cancer in the 1990s, had carried the mutation as well.
The study used a methodology called Big Picture Evidence, which synthesizes decades of research into a single structured narrative, combining perspectives from a geneticist, an endocrinologist, a surgeon, an oncologist, a pathologist and the patient.
“It was a 2-year project, bringing together research histories, patient stories, technical advances, and implementation barriers," said Lucas Leite Cunha, professor at the São Paulo School of Medicine of the Federal University of São Paulo. “This panoramic view allowed us to understand how genetics shapes the entire clinical journey of the patient and their family.”
Vieira's children, now adults, are both studying to become doctors.
The researchers say the next challenge is expanding access to molecular testing beyond major academic centers, particularly in regions with fewer resources. In Brazil, that effort is being led by a research consortium called BRASMEN, which includes the Federal University of São Paulo, the University of São Paulo and the State University of Campinas.
“Expanding access to these tests would allow other families to experience the hope of early intervention,” said Vieira.
Data from FAPESP