“Our findings of rapidly increasing rates of breast cancer in Marin County… serve as a ‘canary in the gold mine’ as regards breast cancer incidence in educated or affluent women.” – Cancer Prevention Institute of California, 2002


In 1994, the Cancer Prevention Institute of California announced that the rate of new breast cancer diagnoses in the San Francisco Bay Area was 50 percent higher than Europe’s and five times higher than Japan’s. The institute claimed that breast cancer was specifically targeting affluent white women. The San Francisco Chronicle headlined that Marin County had the highest rate of breast cancer on earth.

Women throughout the Bay Area mobilized, demanding answers from the state and federal governments. In Marin, they formed Marin Breast Cancer Watch, later dubbed Zero Breast Cancer. The group called for an investigation into environmental causes, suspecting that Marin might be harboring a radioactive military installation or a toxic dump like New York’s Love Canal. University and nonprofit researchers launched more than 40 studies of breast cancer in the Bay Area.

In 1997, at the urging of local politicians, Congress ordered the Centers for Disease Control to find the cause of the extraordinary rates.

The next year, the Cancer Prevention Institute reported an astronomical rise in breast cancer incidence rates in San Francisco’s Bayview-Hunters Point neighborhood, a primarily black community laced with toxic sites targeted for cleanup by the Environmental Protection Agency.

But the institute’s report said the elevated rates were not caused by environmental carcinogens; instead, they were an artifact of breast cancer screening. “An increase in the amount of mammography being done among a group of women can lead to a temporary increase in the breast cancer incidence rate,” the authors wrote.

The report dismissed the toxic sites and socioeconomic and lifestyle factors as explanatory, squarely blaming the high rate on a jump in the number of mammograms resulting from breast cancer screening programs begun several years earlier.

When a mammography outreach program is first introduced to a population, it quickly identifies already existing cancers and cellular abnormalities. As screening progresses, the rate of new diagnoses shoots up sharply, and then gradually falls due to the “screening saturation effect.”

In short, the number of new diagnoses decreases as the population is increasingly “saturated” with screening and the pre-existing pool of disease is discovered.

Indeed, after an initial jump, the breast cancer incidence rate in Bayview-Hunters Point dropped—as it did in Marin and elsewhere in the country in the years following the introduction of community screening programs.

A few months after releasing its Bayview-Hunter’s Point study, the Cancer Prevention Institute reported that the breast cancer incidence rate for white women in Marin was 9 percent higher than the state average.

In a theoretical about-face, the institute proposed that the lifestyles of the “generally very affluent and well-educated” women in Marin were responsible for the high rate. The authors left open the possibility that an unknown factor in the environment could be causing the excessive number of breast cancers. (Although a 2002 study by the institute dismissed exposure to environmental toxins in Marin as possibly causal.)

In a single sentence, the authors—epidemiologists Dee West and Angela Prehn—acknowledged that Marin’s incidence rates could be tied to a greater-than-average use of mammography. But they did not explore that avenue.

So, what the institute found responsible for high rates in Bayview-Hunters Point—an increase in mammograms—was discarded for Marin.

Dr. West, who headed the cancer registry’s Bay Area operations from 1986 to 2005, declined to comment on why.


Report to Congress

In May 1998, the Centers for Disease Control released its report to Congress. The agency found that the high breast cancer incidence rate for affluent white women in the Bay Area was caused by “the higher use of mammography, i.e. the greater number of women screened, the greater number of breast cancers detected.”

The C.D.C. pointed out that if breast cancer was disproportionately afflicting these women, their death rates from breast cancer would have increased over time. But mortality rates for Bay Area white women were flat or slightly declining.

Mortality rates for black women—in the Bay Area and nationwide—were not declining. In fact, the breast cancer mortality rate for black women has far exceeded the rate for white women for decades, despite lower incidence rates among blacks.

The C.D.C. attributed that low incidence rate for black women and women living in poverty to lesser access to the screening programs, which are known to result in overdiagnosis and inflated incidence rates.

The finding concurred with existing studies on the inefficiency of using mammography as a cancer prophylactic. And it attributed the higher mortality rate for blacks and Latinas to inferior access to cancer treatment after symptoms present clinically.

The C.D.C.’s report also criticized the Cancer Prevention Institute’s theory that environmental and lifestyle factors were somehow increasing the risk of breast cancer in Marin. The agency “cautioned” that the institute’s “conclusions regarding the risk for breast cancer … could not be assessed with the [epidemiological] methods used.”

And the trajectory of Marin’s incidence rates, said the agency, were comparable with national rates.

Going further, the agency singled out as non-explanatory the lifestyle factors the institute proposed as explanatory of the elevated rates: having children later in life, breast-feeding less, drinking slightly above-average amounts of alcohol and the earlier-than-normal onset of puberty and later-than-normal onset of menopause.

The report dismissed these explanations on the basis that they were not backed up by empirical data or able to account for fluctuations in incidence rates and for falling death rates.

The C.D.C. also took aim at the institute’s management of the Bay Area arm of the state cancer registry. The report noted that the regional registry’s breast cancer data is often incomplete and suffers from an absence of follow-up on diagnoses.

Language barriers and the “prohibitive” cost of collecting enough data to determine the fate of patients also threatened the registry’s statistical accuracy, the report said.

Wizened by their experience in the cauldron of Bay Area politics, the authors aptly concluded: “Concerned citizens may interpret the findings [as] an attempt to cover up known risks.”

Indeed, a few months after releasing the report, the C.D.C. hosted a community meeting in San Francisco. On Sept. 1, 1998, dozens of local scientists, politicians and breast cancer activists lined up to kill the messenger.

Wendel Brummer was the director of public health for Contra Costa County when he rallied Bay Area epidemiologists against the agency by likening breast cancer incidence in the Bay Area to an “Ebola outbreak in Manhattan.”

“The Bay Area [has] the highest rate of breast cancer identified anywhere on the planet [and] Marin County [has] the Bay Area’s highest rate of breast cancer, yet it is as unpolluted a populated area as you can find in the country,” he said at the meeting. “Incredibly, the C.D.C. acted as if its main mission was to pacify women, rather than find the cause of the disease.”

A consortium of breast cancer activists and top officials at Bay Area health departments issued a formal rebuttal to the C.D.C.’s report.

The rebuttal decried the agency’s comparison of the incidence rates of black women to white women as an attempt to weaken the statistical power of what they perceived as an ongoing epidemic of breast cancer that preferred white women.

“Since the Bay Area has large numbers of women of color with lower incidence rates, comparisons of incidence need to be made between white women only,” the consortium wrote. “Inclusions of other ethnic groups gives the [C.D.C.’s] predicted lowered incidence for the Bay Area and provides a false reading of an actual situation.”

In their decision to ignore the prevailing evidence, the outraged scientists, activists and public health officials set the future course of Bay Area breast cancer research—to the detriment of all women, but particularly to impoverished women of color.

For their part, Bay Area media outlets trumpeted Dr. Brummer’s accusation that the C.D.C.’s report to Congress was a whitewash. They paid little attention to the agency’s finding that the high incidence rates were an artifact of mammography and poor science.

Relying on interviews with Cancer Prevention Institute staff, a 2000 article in the Chronicle framed an absurdly circular statement as fact: “Part of the reason Marin’s rates are so high is simple: Breast cancer is far more common among white women than minorities and Marin has a high proportion of white women.”


To the gold mine

The monetary stakes were high. The federal government alone doles out more than $1 billion a year for breast cancer research. The Cancer Prevention Institute has received tens of millions of dollars in federal and state funds to collect and study cancer incidence data, including searching for the cause of Marin’s (non-existent) breast cancer cluster. Unfortunately, the institute has consistently bypassed the simplest explanation that fits the evidence.

In 2002, institute researchers Christina Clarke, Sally Glaser and Dr. West published a peer-reviewed paper that expanded upon what we call the “Marin Syndrome,” concluding that all middle-aged white women in Marin County “experienced a marked increase in breast cancer rates between 1991 and 1997.”

The “reasons remain unclear,” they wrote, but the increasingly high rates “did not appear to be due to screening mammography or environmental exposures [and] the finding may signal a rising risk of breast cancer in this demographic group.”

In 2002, the institute, along with epidemiologists from Marin Health and Human Services, the University of California, San Francisco and an activist from Zero Breast Cancer, co-authored a political bombshell titled “Breast Cancer Incidence and Mortality Trends in an Affluent Population, Marin County, California, USA, 1990-1999.”

“The media has pronounced Marin County ‘the breast cancer capital of the world,’” the study began. It made no mention of the C.D.C.’s evisceration of that notion.

Instead, it introduced an explosive new claim that relied on cancer registry data gathered by the institute: “Incidence rates of invasive breast cancer among white women in Marin County show a distinctly increasing trend. Rates increased 37% in Marin … but only increased 3% in the rest of the San Francisco Bay Area and other urban counties.”

For Marin women between ages 45 and 64, the rate of increase was a breathtaking 79 percent, burdening these women with an incidence rate 72 percent higher than all other urban California counties.

The authors warned, “Marin County statistics indeed serve as a ‘canary in the gold mine’ as regards breast cancer incidence in educated or affluent women, and they may also be prescient as regards breast cancer mortality.”

Then, correctly undercutting their own thesis, the authors observed that breast cancer mortality rates in Marin were lower than in the rest of California. They neglected to note that if breast cancer was truly on the rise for wealthy whites, their death rates from the disease would have had to increase.

The authors speculated that due to the supposed risks associated with never giving birth or with giving birth later in life, white women in Marin must be at the greatest risk of all women anywhere.

Almost as an afterthought, they wrote: “We consider it doubtful that the observed trends are strongly biased by inaccurate cancer registry or population data.”

The study dismissed the idea that the high incidence rates were an artifact of mammography on the basis of a survey conducted by Zero Breast Cancer that found a tiny sample of women in Marin got only “slightly more mammograms than average.” That finding, however, is contradicted by the biannual California Health Interview Survey, a project of the University of California, Los Angeles, which shows that Marin women receive many more mammograms than average.

The “canary in the gold mine” study generated sensational headlines all over California and the nation, including the Chronicle’s “Unseen Killer Stalks Marin.” A Chronicle reporter wrote, “For reasons not completely understood, breast cancer seems to favor educated, well-off women wherever they live.”

Reporters did not bother to interview epidemiologists critical of the finding, such as Stanford University’s Alice Whittemore, who was to publish a critical analysis assessing that the gold mine paper was, “Another example of the political/social/psychological/scientific quandary presented by … a group of activists collaborat[ing] with epidemiologists to investigate the reason for the cluster.”

The problem, Dr. Whittemore said, is that there was no cluster.

It turned out that the population data used by the Cancer Prevention Institute researchers was wrong. Making an elementary error, the researchers had understated the number of middle-aged women living in the county, in turn inflating the rate of increase of breast cancer diagnoses.

Two years after the Cancer Prevention Institute incorrectly reported a 37 percent increase in incidence rates, it quietly recanted. The institute published new figures claiming that the breast cancer incidence rate for women in Marin during the 1990s was 6 percent higher than the Bay Area’s rate and 15 percent higher than the California rate.

High screening rates and chance fluctuations in data gathering can easily account for those incidence rate gaps.

The Light spoke with Christina Clarke of the Cancer Prevention Institute, presenting the scientific arguments that contradict the claim of a breast cancer epidemic. She responded that due to falling incidence rates, there may no longer be an epidemic in Marin.

“Marin women can just go back to being all women who are concerned about breast cancer,” she said.

Then, staking out contradictory positions, Dr. Clarke said that wealthy white women are generally more at risk of breast cancer than poor women of color. She said it is “definitely possible” that Marin’s historically high incidence rates were caused by an increased use of mammography.

Yet she also pointed to excessive alcohol consumption, the delayed or non-bearing of children, and the use of certain types of hormone replacement therapy as the most probable causes of the previously high incidence rates.

Hindsight is a powerful corrective, however. If Marin’s white women had been targeted by an epidemic of breast cancer, their mortality rate from the disease would have increased, but it has greatly decreased during the past 30 years.

Dr. Clarke’s canary in the gold mine is still singing.


Next week, “Busted!” explains how the unproven claim that hormone replacement theory caused breast cancer in Marin—and elsewhere—is faulty, although widely believed.


Read Peter Byrne’s investigative series on a nationwide breast cancer scare that never should have happened: