Plain language summary
Overweight and obesity play a role in the development and potential outcomes in breast cancer. Several factors have been implicated linking cancer and obesity including hormones imbalances and inflammation, however exact links have yet to be elucidated. This systematic review of 4 randomised control trials containing 5234 women aimed to examine obesity related blood factors such as hormones, fats and sugar and their relationship with prognosis in individuals with breast cancer. The results showed that higher levels of testosterone were associated with an increased risk of recurrence of breast cancer. The female sex hormones, oestradiol and sex hormone binding globulin were not associated with breast cancer recurrence. Blood sugar levels and insulin resistance were not associated with breast cancer recurrence. There were certain growth factors, which are molecules responsible for stimulating cellular processes, that were responsible for an increased chance of recurrence of breast cancer and insulin-like growth factor and platelet derived growth factor were shown to increase risk but only when increased in combination with each other. Inconsistent results were seen with C-reactive protein, which is an inflammatory marker. It was concluded that testosterone may be associated with an increased risk of breast cancer recurrence, however the evidence from the other blood factor was unreliable due to poor quality trials. More trials are needed to investigate these factors further. This study could be used by healthcare professionals to understand that weight loss is the key to the prevention of recurrence of breast cancer in those who are overweight and that testosterone levels could be used to identify those who are at an increased risk.
Abstract
Obesity plays an important role in the development and progression of breast cancer via various oncogenic pathways. However, the biological mechanisms underlying this relationship are not fully understood. Moreover, it is unclear whether obesity-related and further associated biomarkers could be suitable targets for lifestyle interventions. This systematic review was conducted to examine relationships between obesity-related blood parameters and prognosis for breast cancer survivors enrolled in lifestyle intervention studies. A systematic, computerized literature search was conducted from inception through August 26th, 2020 in PubMed, EMBASE, and CENTRAL. The focus was on observational data from randomized controlled lifestyle intervention trials investigating associations between selected baseline biomarkers, measured in remission, and breast cancer recurrence, breast cancer mortality and/or all-cause mortality. Four studies with data from 5234 women met the inclusion criteria.Studies herein provide moderate evidence that bioavailable or serum testosterone may be positively linked to breast cancer recurrence and inversely linked to disease-free survival. Limited evidence suggests no associations with circulating estradiol or insulin levels on prognosis outcomes, whereas HDL cholesterol was inversely associated with breast cancer recurrence. For some other biomarkers, such as growth factors, adipokines, and CRP, the evidence for associations with disease prognosis was too weak to draw conclusions.Overall, despite potential candidates, there is insufficient evidence to confirm or refute that obesity-related biomarkers and sex hormones have a prognostic value for breast cancer survival. More longitudinal studies in breast cancer survivors to examine the clinical utility of obesity-related biomarkers are needed.
Methodological quality
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