Background: Physical activity (PA) before and after breast cancer diagnosis has been reported to be associated\nwith lower mortality. However, whether changes in the activity after diagnosis impact prognosis is unclear and has\nnot received much attention. This study aimed to examine pre- to postdiagnosis leisure-time PA and breast cancer\nprognosis.\nMethods: We used data from the MARIE study, a prospective population-based patient cohort study of 3813\npostmenopausal breast cancer patients, aged 50-74 at diagnosis, recruited from 2002 to 2005, re-interviewed in\n2009, and followed up until June 2015. Prediagnosis PA was assessed at recruitment; postdiagnosis PA was assessed\nat re-interview in 2009. To examine pre- to postdiagnosis change in PA, women were categorized by pre- and\npostdiagnosis PA using a cut-off of 7.5 MET-h/week for meeting PA recommendations and combined into four\ngroups: insufficiently active, increasingly active, decreasingly active, and sufficiently active. Cox regression models\nwith delayed entry were used to assess associations between pre- to postdiagnosis patterns of PA and overall\nmortality (OM), breast cancer mortality (BCM), and recurrence-free survival (RFS). Additional analyses of pre- and\npostdiagnosis PA (no activity (reference), low activity, sufficient activity) with cancer outcomes, such as using a timedependent\nmodel, were performed. In total, 2042 patients were included in the analyses.\nResults: There were 206 deaths (114 from breast cancer) after a median follow-up time of 6.0 years after the 2009\ninterview. Compared to insufficiently active women, increasingly active women were at lower risk of OM, BCM, and\nRFS (HR (95%CI) of 0.50 (0.31-0.82), 0.54 (0.30-1.00), 0.58 (0.40-0.84), respectively). In sufficiently active women,\nassociations for OM (0.75 (0.48-1.15)), BCM (0.61 (0.33-1.13)), and RFS 0.80 (0.57-1.14)) were similar to increasingly\nactive women but attenuated, and decreasingly active women were not at lower risk for OM (0.91 (0.61-1.36)), BCM\n(0.80 (0.45-1.42)), and RFS (1.04 (0.76-1.43)). In time-dependent analyses, sufficient activity vs. no activity was\nassociated with better OM (0.73 (0.57-0.93)), BCM (0.64 (0.46-0.89)), and RFS (0.82 (0.68-0.99)). Low activity was not\nsignificantly associated with prognosis.\nConclusion: Our data support benefits for breast cancer prognosis in being physically active pre- and postdiagnosis\nparticularly for women who were insufficiently active prediagnosis.
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