It turns out that both her ovarian cancer and her breast cancer were caused by that gene. It also turns out that cancer specialists have known for many years - long before they had pinpointed the gene, called BRCA1 - that women with family histories such as Marks' were at high risk.
As will be the case with most of the 26,800 women who will be diagnosed with ovarian cancer this year, Marks' disease was detected after it had spread far beyond her ovaries.
Now she is fighting for her life with a grinding marathon of surgery, chemotherapy and radiation. She also is fighting to raise awareness.
The main reasons that ovarian cancer is diagnosed so late are that it has no distinctive early-warning symptoms and no proven screening test. But another reason, Marks and other fighters say, is ignorance and complacency among women and their doctors.
Too many women are uninformed about subtle clues - including family history - and do not know that there are tests, albeit imperfect ones, that can help them stay on guard.
As a founding member of the National Ovarian Cancer Coalition, Marks is part of a nascent movement dedicated to ``breaking the silence.''
``Ovarian cancer has been called the silent killer,'' Marks said. ``It isn't silent; it whispers. And doctors need to learn to listen. And women need to learn to be aware of symptoms that could possibly be ovarian cancer.''
* Carolyn Marks' home, an airy retreat perched on a hill overlooking the lake in Peace Valley Park, showcases her personality, from the bright print couches to the book Thank God It's Only Cancer on the coffee table.
On a recent morning, she looked slim and stylish in a dark-purple blazer, glittery scarf and black hat.
She makes the fight look easy, but it is not.
Every morning, she must ``face the losses'' - the hidden scars, the missing organs, the hair surrendered to chemotherapy.
``It's a featureless face when you have no hair,'' she said, ``so I take the time to put on eyebrows and eyelashes and my wig. But I'm just trying to look human, not alien.''
When she was first diagnosed with ovarian cancer, she was frightened but confident. Though the disease had reached the 12th of 13 substages - though only a quarter of late-stage patients survive five years - she believed that the standard treatments would soon send her into remission.
``But, somehow, it all began to sound like a Hertz commercial - where there's Hertz and there's 'not exactly,' '' Marks recalled. ``After the surgery and the first six chemo treatments, I asked, `Well, is it gone yet?' `Not exactly. It still seems to be in the lymph nodes in your abdomen.' ''
Her breast cancer, in contrast, had not spread to any lymph nodes.
It struck in 1973, when she was only 27. Marks, who grew up outside New York, and then-boyfriend Steven Gratz were on vacation, taking a break before their big move to his hometown, Philadelphia. They were leaving teaching jobs in Broward County, Fla.
When she felt the large, surprising lump in her right breast, she was inclined to dismiss it as hormonal. Gratz insisted that she see a doctor in Philadelphia.
Within days, she underwent a mastectomy.
She was shockingly young - the median age for breast-cancer diagnosis is 65 - but she discovered that an aunt had died of breast cancer at the same age.
Suddenly, instead of career and courting issues, she and Gratz were grappling with life-shattering facts: Despite disfiguring surgery, the cancer could come back in her healthy breast, and since the hormonal changes of pregnancy might trigger a recurrence, having children would be risky.
``There was no one my age to talk to,'' she said. ``There were no support groups. That's when I realized I really had to figure out how I could structure my life with this hanging over my head.''
Her Temple University Hospital surgeon warned her that Gratz, too, had a lot to figure out.
``He said to me, `How well do you know this guy Steve?' I said, `Not this well.' He said, `Let me tell you, I've seen husbands who can't stay by their wives during this. They fall apart.'
``Well,'' Marks said, smiling fondly, ``Steve obviously not only hung in there but has been a wonderful source of support.''
Gratz, now an assistant principal at Philadelphia's High School of Engineering and Sciences, said the only thing he feared was losing her.
``I was going to be there for her no matter what happened,'' he said. ``. . . The most important thing was getting her healthy again.''
Although they soon married, it was not until four years after her mastectomy that they felt free of the threat of recurrence. Marks took the bold step, unusual back then, of having her healthy breast removed. Then she had reconstructive surgery on both breasts.
Their son, Joel Gratz, now a bright, athletic and musically talented 15-year-old, was born in 1981.
Over the next decade, Marks forged ahead on all fronts. She rose in the ranks from a personnel job to director of management training at Temple. She earned her doctorate and became executive director of the PENJERDEL Employee Benefits Association.
She also served as president of the Bucks chapter of the National Organization for Women and the Bucks County Women's Fund, a charity dedicated to ``improving choices and chances'' for women. Plus, she was a delegate to the 1988 Democratic National Convention.
But her crowning achievement, she said, was setting up her own management-consulting business - Carolyn A. Marks & Associates - in 1989 and quickly landing a large contract.
``Carolyn is an alchemist,'' Geri Danzig, a close friend and neighbor, said. ``She seems to have the power to transform things - whether it's herself or an organization or a mission.''
In 1994, Marks felt up to any challenge she could imagine.
That's when cancer hit again.
* Ovarian cancer is rare. A woman's lifetime risk is one in 70, compared to one in eight for breast cancer.
But while ovarian cancer will strike about one-seventh as many American women as breast cancer this year, it will kill 14,200 - a third as many as breast cancer.
Breast cancer gets 10 times more research funding than does ovarian cancer, partly, experts say, because ovarian cancer kills so many of those who might lobby for more money.
``I have said many times that I feel ovarian cancer is the forgotten women's cancer,'' said Dr. Robert M. Young, president of the Fox Chase Cancer Center, a leader in ovarian-cancer research.
Ovarian cancer is not inherently more lethal. If treated - with surgery and platinum-based drug therapy - while confined to the ovaries, its five-year survival rate is better than 90 percent. But only a quarter of all cases are caught that early.
Even with early diagnosis, many women die because of substandard treatment. A National Cancer Institute study published last year found that 90 percent of early-stage cancer patients did not get optimal treatment, typically because their surgeon failed to sample lymph nodes for signs that the cancer had spread.
The bottom line: Even with powerful new chemotherapies, less than half of all ovarian-cancer patients survive five years - not much better than a century ago.
Ovarian cancer is insidious. Even before symptoms or a tangible tumor develops, it can release cells that float in the abdominal fluid and attack other organs and structures.
In early stages, women sometimes have vague, inexplicable pelvic pressure, indigestion or bloating. In later stages, there may be obvious symptoms - nausea, vomiting, constipation, a swollen abdomen - that many doctors do not connect with ovarian cancer. (Witness the example of comedian and ovarian-cancer statistic Gilda Radner.)
Marks had no symptoms until her tumor was so big that her doctor felt something during a routine pelvic exam. She said he told her that he figured it was a common, benign fibroid and that she need not worry, despite her breast-cancer history.
After pushing for four months for a more definitive diagnosis, she added, she was given an ultrasound that immediately revealed a suspicious mass.
Historically, the manual pelvic exam has been the only detection method. Technology has added ultrasound, which bounces sound waves off the reproductive organs, and CA125, a blood test that measures levels of a protein shed by tumors.
The problem is that ultrasound results can be tricky to interpret. And half of all women with early-stage cancer do not have elevated CA125 levels, while many women with benign tumors do.
As a result, the conventional wisdom is that routine screening does not work. Indeed, three years ago, a panel of the National Institutes of Health concluded that there was no evidence that annual screening using ultrasound and CA125 benefited women or reduced mortality rates.
The panel, however, did recommend that women with two or more ovarian-cancer cases in their families get screened anyway.
And it advised that after completing childbearing, ``or at least by age 35,'' high-risk women should have their ovaries removed - a gambit that triggers menopause.
Marks and other activists challenge the idea that screening is futile - and so does new research. In England, for example, a five-year study led by Dr. Ian Jacobs found CA125 to be highly reliable in flagging cancer.
The key, the study showed, was monitoring increases in CA125 levels over time, rather than waiting for it to reach an abnormally high level. Jacobs has launched a much larger trial that he hopes will definitively show that mortality rates can be reduced by a third.
But survivor groups - a growing list that includes Gilda's Club, the Ovarian Cancer Research Fund, Ovarian Plus International, and the National Ovarian Cancer Coalition - say detection must complement education.
Through pamphlets, hotlines and Web sites, they are crying out against their ``silent'' foe, telling women - and their doctors - the facts: that long-term birth-control use decreases ovarian-cancer risk by reducing ovulation; that not having children, having breast cancer, and using talcum powder on the genital area, among other factors, increase the risk; and that genetics can play a powerful role in ovarian cancer, especially for women of Ashkenazi Jewish ancestry, because BRCA1 mutations are more common in this group.
Marks discovered that she carried a mutated BRCA1 only after she heard about genetic testing at the Fox Chase Cancer Center and pursued it.
Although BRCA1 mutations are believed to account for only 5 percent of breast cancers and 11 percent of ovarian cancers, the risks are high for carriers: a 53-to-85-percent chance of breast cancer, a 16-to-60-percent chance of ovarian cancer.
''All these women who have had breast cancer have got to get to doctors who know how to look for this link,'' Marks said.
* The first rounds of chemotherapy were not enough to trigger a remission, so the dosage was doubled.
Weak and exhausted, Marks was confident the cancer must be gone.
``Not exactly'' came the answer.
In early 1995, her doctor candidly told her that she would need chemotherapy indefinitely. The toxic drugs were only suppressing, not wiping out, the cancer, even as they weakened her bone marrow, the core of her immune system.
She was devastated but undaunted.
``That was when the celebration gene kicked in,'' she said.
In between her treatments, 200 friends threw her a gala 50th birthday party. Then came Europe - via the Concorde - a cruise to Alaska, and her mother's 80th birthday in Florida.
Still, the cancer advanced, first to more lymph nodes, then to her colon. She fought back with radiation and new drugs, hoping to hear that it was gone, but the answer was always the same: ''Not exactly.''
Gradually, her optimism faded. She flirted with despair. She asked her family and friends: What kind of life is this?
But it was simply not in her nature to withdraw or give up.
Instead, she developed an operating plan for a county victim-assistance program, began studying to become a bas mitzvah - a ritual denied to girls when she was a teenager - and joined the long-range planning group at her synagogue, kidding fellow members that appointing her was ``a new definition of optimism.''
She also became a force in the National Ovarian Cancer Coalition, led by Gail Hayward, 55, of Boca Raton, Fla. Hayward recently called Marks ``a godsend'' and praised her for developing a strategic plan and getting corporate funding for the group.
In February, despite ongoing treatment, Marks represented the coalition before a federal-government panel seeking advice on handing out a new $7 million ovarian-cancer research grant.
In March, she took center stage again when 13 Bucks County women's organizations honored her with their annual leadership award. Her story, she told them, has ``a happy ending.''
``All the while I was kvetching about not having a life,'' she said, ``I discovered I was doing three things that helped me not only to survive but thrive: I've learned how to stay connected, get involved and hold on to hope.
''So am I cured?
``But I am healed - and very fortunate.''