In his series for the Point Reyes Light, Peter Byrne took a close look at claims of a breast cancer epidemic among white women in upscale Marin County and found that widespread cancer screening, producing many false positives, is the likely cause of a feared “cancer cluster” in the county. He reported that many non-cancerous findings are erroneously entered in the state’s cancer registry as cancerous. “There is not more breast cancer in Marin than elsewhere, experts say; rather, it is detected more frequently—and often erroneously,” Byrne wrote. “Over the decades, the persistent belief that wealthy white women are more at risk of breast cancer has skewed research priorities and undermined the effectiveness of public health activities around the nation.” In Marin, the county health department excluded non-white women from most of its studies on breast cancer causation, Byrne found, and bypassed data disproving its conclusions. He quoted experts elsewhere who argue that Marin’s high incidence rate is a statistical anomaly caused by sociological factors. The more screenings a woman gets, “the more likely she is to be called back for a second mammogram or to be falsely diagnosed with cancer,” Byrne wrote.  He recounted the case of one woman whose misdiagnosis led to an unnecessary mastectomy. When the woman sought her records at the California Cancer Registry, she found that the abstract was missing vital information and contained substantial mistakes. Byrne, who obtained a series of internal audits and progress reports on the registry, concluded that its chronic data-quality problems are worsening. “Peter Byrne’s reporting is exhaustive, showing how a local reporter working on a subject of intense local interest can shed new light on global issues of cancer, misdiagnosis and medical misreporting,” said Robert Lee Hotz of The Wall Street Journal