Medical researchers trying to unlock the mystery of Marin County’s high incidence of breast cancer now suspect that Marin women’s use of estrogen and progesterone to treat menopausal symptoms was likely a major factor.Use of combined hormone therapy dropped significantly nationwide after the release in 2002 of a study demonstrating a strong association between the therapy and breast cancer risk.
“Women literally quit hormone therapy like it was a bad habit overnight,” said Christina Clarke, a research scientist with the Northern California Cancer Center in Union City. “We saw a huge drop-off in Marin and shortly thereafter we saw a big drop-off in breast cancer rates.
“We continue to see an excess of breast cancer in the Bay Area, and in Marin County in particular, but it is not as extreme of an excess as we saw before,” Clarke said.
From 2003 to 2007, the most recent years for which data are available, the rate of breast cancer in Marin averaged 150.9 cases per 100,000 women per year among nonHispanic white women. That compared with rates of 141.7 cases for the same group of women throughout the Bay Area and 137.9 cases across California. From 2002 to 2006, the rate of breast cancer throughout the United States was 134 cases per 100,000 women per year among nonHispanic, white women.