Changes in Physical Activity Across Cancer Diagnosis and Treatment Based on Smartphone Step Count Data Linked to a Japanese Claims Database: Retrospective Cohort Study - Yoshihide Inayama; Ken Yamaguchi; Kayoko Mizuno; Sachiko Tanaka-Mizuno; Ayami Koike; Nozomi Higashiyama; Mana Taki; Koji Yamanoi; Ryusuke Murakami; Junzo Hamanishi; Satomi Yoshida; Masaki Mandai; et al. (JMIR Cancer)