The symptoms started a little before my 50th birthday in December. I pride myself on healthy living, and my gauge of good health has always been consistency: are sleep, eating, digestion and period cycle regular? Now the clockwork was off, if only slightly. My hypervigilance was born more than a decade earlier in Hong Kong, where I lived from 2009 to 2013 while working as a journalist. In 2013, at age 37 with no family history, I was treated for stage 0 breast cancer – the earliest detectable...