When Nancy M. Cappello learned that she had breast cancer, and that mammography could not find it, she turned her misfortune into a tireless campaign that led 36 states to require fuller disclosure to women about their mammogram results and the limitations of the test.
Her illness — breast cancer that was not diagnosed until it had reached an advanced stage and required chemotherapy — was exactly what she had spent more than a decade trying to help other women avoid. So was her treatment-related death.
Dr. Cappello, who was 66, died on Nov. 15 at Waterbury Hospital in Connecticut. Her husband, Joseph J. Cappello, said the cause was an infection related to myelodysplastic syndrome, a rare blood cancer caused by the chemotherapy and radiation she received in 2004.
Her activism took root in 2003, when her doctor felt a lump in her breast. Dr. Cappello, a special-education teacher and administrator, had had a mammogram just six weeks earlier, with normal results. A repeat mammogram still showed no lump.
But ultrasound found one — nearly an inch in diameter — and subsequent tests revealed cancer that had already spread to 13 lymph nodes. The stage was 3c, considered an advanced form of the disease, though it had not spread to other organs.
Dr. Cappello needed a mastectomy and an arduous course of chemotherapy and radiation.
When she asked why mammography had not found the tumor, her doctors explained that she had so-called dense breast tissue, which had hidden the cancer from the X-rays. No one had ever told her that before; she had never even heard of such a condition.
Dense breasts have a high proportion of glandular or connective tissue, which blocks X-rays. Breasts that are not dense have more fat, which X-rays penetrate easily.
Dense tissue makes cancer harder to find because the tissue and tumors both show up as white on mammograms and blend together. Fat looks black, so tumors stand out more in fatty breasts.
Dense tissue, for reasons not fully understood, also increases the risk that cancer will develop.
Dr. Cappello was outraged that she had never been informed of the condition and the risks it posed. She had been having regular mammograms for 10 years. She thought she was in the clear.
In a 2012 interview with The New York Times, she said that had she known about her dense tissue and the shortcomings of mammography, she would have requested ultrasound or M.R.I. scans, which are better than mammograms at finding tumors in dense breasts.
And if she had had those other tests, she believed, her cancer would have been found at an earlier stage, and she might not have even needed chemotherapy. Because the tumor was so large, she thought it must have been growing for four or five years.
She urged her doctors to begin telling women if they had dense breasts. But they told her that that was not part of the “standard protocol,” she said, and declined.
“We said, ‘Then we’re going to make you do it — this is life and death,’” Mr. Cappello said in an interview, referring to himself and his wife.
The couple learned that dense breasts are not rare: They occur in about 40 percent of women who have mammograms. The condition is more common in younger women, but some older women have it as well. It shows up only on mammograms and cannot be detected by touch.
The Cappellos approached state legislators and enlisted medical experts to help make their case. It took time, but in 2009 Connecticut became the first state to require that women be told if they had dense breasts and that insurance companies cover ultrasound scans for those women.
After that, Mr. Cappello said, women from around the country began to contact Dr. Cappello, asking how they could get similar laws passed in their states. She quit her state job and founded nonprofit education and advocacy groups, both called Are You Dense?
Donna Johnson, the groups’ board president, said that thousands of women called for information and advice over the years, and that Dr. Cappello had personally returned every call.
Dr. Cappello testified before state legislatures and addressed medical conferences in the United States, Japan, France, Italy and Canada.
“She eventually gained influence and support in the medical community,” Mr. Cappello said, “because she was right, and she wasn’t going away.”
Some in the medical profession objected, arguing that not all women with dense tissue have the same increased risk of breast cancer, and that reporting the condition could frighten women and lead to a flood of unnecessary screening tests and biopsies. Doctors also said many of the state-mandated letters were too hard for patients to understand.
Dr. Cappello never wavered from her conviction that women had the right to know, and to decide for themselves whether to act on the information.
She was born Nancy Marcucci in Waterbury on Oct. 30, 1952. Her father, Stephen A. Marcucci, owned a plumbing and oil business, and her mother, Antoinette (Llorens) Marcucci, was a homemaker.
She attended Watertown High School in Connecticut and earned bachelor’s and master’s degrees in education and special education from Central Connecticut State University. She went on to obtain a doctorate in educational administration from the University of Connecticut.
She married Mr. Cappello, now a retired real estate broker and distributor of percussion instruments, in 1974.
From that year until 1988 she was a special-education teacher in Watertown for students with learning, emotional and intellectual disabilities. She became director of special education there and consulted for the state education department, which she led as interim bureau chief in 2007. She retired from the department in 2009 to devote full time to advocacy and education.
In addition to her husband, she is survived by her mother; her sister, Angela Boratko; and her brothers, Stephen and Mark Marcucci.
Dr. Cappello was well until late summer. Her blood cancer was diagnosed in September. The best hope for a cure was a bone-marrow transplant. Doctors found a perfect match, and the transplant was scheduled for December. But her health declined rapidly. She needed repeated transfusions, contracted infections and ran high fevers.
An infection with bacteria called Clostridium difficile — very likely caused by extensive treatment with antibiotics, which disrupt the normal balance of microbes in the intestine — led to septic shock and her death.
Without Dr. Capello’s leadership, Ms. Johnson said, the organization she founded is struggling to regroup. “We have,” she said, “14 states to go.”
