Circadian Disruption and Breast Cancer

The author responds: I will respond to 3 aspects of Tarone's letter. First, I was neither misleading nor incorrect in writing that riskof breast cancer “is increasing everywhere.”1 Incidence, which reflects “risk”, has increased in all areas for which reliable data exist over time,2 and these increases have been greatest in areas with historically low risk.2,3 Introduction of mass screening probably had little or no effect on incidence increases in developing countries.2 After adjustment for screening in the Nordic countries, incidence in each of them was still found to have increased from 1978 to 1997.4 In the U.S., screening accounts for some, but not all of the increasing incidence.5 Mortality is increasing in much of the world, although among those Western countries with historically high death rates it has recently begun to decline.2,3 Jatoi and Miller6 argue that the primary reason is improved therapy. Second, Tarone claims that “risk” is decreasing for young women. He has confused mortality for incidence. From his paper in 1996,7 Figure 3 shows a slight increase in incidence in white women aged 40–49 and in those aged 30–39 from 1973 to 1993 in the United States. In the latest SEER data,8 incidence in women 49 and younger went from 40.7 per 100,000 in 1975 to 42.6 in 2002. Mortality has declined, and as Chu et al7 state, “Thus, medical interventions, such as early detection and successful treatment, are the most probable sources for the declines in breast cancer mortality.” Tarone and colleagues9 have furthered these analyses and made a variety of speculations (eg, increasing proportion of obese women, yet also increasing proportion of physically active women born since WWII) on this mortality decline in younger age groups of women.10 A discussion of this was beyond the scope of my paper,1 and in no sense invalidates any of my statements therein. Finally, Tarone's closing paragraph, in which he asserts that “EMF” exposure is not a risk factor for breast cancer, is a non sequitur. The global rise in breast cancer is a profound mystery. Is it the sum of many known factors, or is it driven by exposures as yet unknown and unimagined? Richard Stevens University of Connecticut Health Center Farmington, CT [email protected]