Is female breast cancer mortality in Japan declining or still increasing? A request for clarification

To the Editor: The recent article by Katanoda et al. provides an important overview of international cancer mortality trends and Japan’s progress and remaining challenges in cancer control [1]. The authors should be commended for addressing this important public health issue. However, I would like to raise a concern regarding the interpretation of female breast cancer mortality trends in Japan. The authors state that mortality from female breast cancer in Japan has ‘declined only slowly or continued to rise,’ and later describe ‘slow declines or continued increases’ in mortality. I find these statements difficult to reconcile both epidemiologically and conceptually. A mortality trend cannot simultaneously be interpreted as a decline and an increase. Consequently, readers may find it unclear whether the authors believe that breast cancer mortality in Japan is currently decreasing, increasing, or remaining essentially unchanged. More importantly, the available evidence suggests that a reduction in breast cancer mortality has not yet been demonstrated in Japan despite more than two decades of population-based mammography screening. In a recent review, it was noted that ‘no reduction in breast cancer mortality has been evident’ following the implementation of organized mammography screening in Japan, and that mortality rates have continued to increase over time [2]. Similarly, it has been emphasized that Japan has not observed a corresponding decline in breast cancer mortality despite ˃20 years of screening mammography implementation [3].