By Joan Biskupic, CNN legal analyst & Supreme Court biographer

(CNN) -- Sandra Day O'Connor, the first woman on the US Supreme Court, opened up about the personal anguish of breast cancer five years after surviving it. Then she went public about the effects of her husband's Alzheimer's disease, including his affection for another woman.

Now, perhaps fitting of the pioneering tendency she has shown all around, the 88-year-old retired justice revealed on Tuesday that she is in "the beginning stages of dementia, probably Alzheimer's disease."

In the letter written from Phoenix, as she explained that she was no longer participating in public life, she again surmounted the stigma that sometimes comes with illness.

"While the final chapter of my life with dementia may be trying, nothing has diminished my gratitude and deep appreciation for the countless blessings in my life," she wrote in the letter released by the Supreme Court.

O'Connor, who became an influential author of decisions on abortion rights, racial affirmative action, criminal procedures, and an array of social dilemmas during her quarter century tenure, also has had a deep personal imprint on American life.

In 1994, when O'Connor first revealed her feelings about surviving the breast cancer discovered in 1988, she observed that people sometimes refused to name the illness, calling it ominously, "the big C." At the time of her surgery, she had not wanted word of her mastectomy and treatment to be publicly disclosed.

Over time, O'Connor said she realized that sharing her story helped other women and eased her own experience with the illness that remained at the fore of her thinking every day.

"Having this disease made me more aware than ever before of the transitory nature of life here on Earth, of my own life," she said in a speech to the National Coalition for Cancer Survivorship in 1994. "And it made me value each and every day of life more than ever before."

When O'Connor, a justice since 1981, stepped down in January 2006, her retirement was prompted by the dementia of her husband, John. The couple had met while at Stanford Law School, married in 1952 and raised three sons. John gave up prominence as a Phoenix attorney and moved to Washington when President Ronald Reagan selected the former Arizona state senator and judge for the high court.

Less than two years after her retirement from the bench, O'Connor let it be known that John had found a new romance in his care facility in Arizona, an occurrence not uncommon with Alzheimer patients who forget their spouses.

At the time, O'Connor's eldest son, Scott, told a local TV station, "Mom was thrilled that Dad was relaxed and happy and comfortable living here and wasn't complaining." Alzheimer's advocates commended Justice O'Connor and her family for raising awareness and reducing the stigma of the disease.

John died in 2009 at age 79.

In recent years, O'Connor had withdrawn from her special projects, including the iCivics program she helped found to teach students about civics principles. She was living in a care facility. The retirement chambers she had maintained at the Supreme Court in Washington was closed out this summer. Retired Justice Anthony Kennedy now occupies the suite.

"I can no longer help lead this cause, due to my physical condition," O'Connor said of her civics work in the letter released Tuesday. "It is time for new leaders to make civic learning and civic engagement a reality for all."

The trailblazer concluded, "I hope that I have inspired young people about civic engagement and helped pave the pathway for women who may have faced obstacles pursing their careers."