The very public split between longtime partners Planned Parenthood and the Susan G. Komen for the Cure foundation foretold how abortion could be a pivotal issue in November's presidential and congressional elections.
More than $400,000 has so far been pledged online by 6,000 donors, a day after the row broke out, on top of $250,000 from Texas oil baron Lee Fikes and his wife Amy to set up a Planned Parenthood Breast Health Fund.
"People respond powerfully when they see politics interfering with women's health," said a spokesman for Planned Parenthood, which offers both abortions and breast screenings for less well-off American women.
"That's why we've seen a tremendous outpouring of support."
Komen was founded in 1982 by Nancy Brinker, a prominent Republican and US ambassador to Hungary under former president George W. Bush, in memory of her sister, who died of breast cancer at age 36.
It famously came up with pink-ribbon logo of the worldwide quest for a cure for breast cancer, and for years it helped underwrite breast screening at Planned Parenthood clinics, including $680,000 last year.
In a statement Wednesday, Planned Parenthood -- the biggest single abortion provider in the United States -- alleged that "anti-choice groups" had been leaning hard on the Komen foundation to cease funding.
"We are alarmed and saddened that the Susan G. Komen for the Cure Foundation appears to have succumbed to political pressure," its president Cecile Richards said.
"Our greatest desire is for Komen to reconsider this policy and recommit to the partnership on which so many women count," she said.
In a video posted on YouTube, Brinker denounced "scurrilous rumors" and "mischaracterizations" of what she called Komen's decision to tightened up its grant-giving and avoid "duplicative" contributions.
"Regrettably, this strategic shift will affect any number of our longstanding partners," she said, "but we have always done what is right for our organization, our donors and our volunteers."
"We will never bow to political pressure," added Brinker, who is currently goodwill ambassador for cancer control for the World Health Organization. "We will always stand firm in our goal to end breast cancer."