Report numbers in each exposure category, or summary measures of exposure
The numbers in each exposure category are stated in Table 2.
(a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, 95% confidence interval). Make clear which confounders were adjusted for and why they were included
The unadjusted estimates (univariate) and confounder-adjusted estimates (multivariate) and their precision are stated in Table 3.
(b) Report category boundaries when continuous variables were categorized
There is no any continuous variable thus no process of categorization and no categories boundaries. The variables in the research are mostly binary variables. If there are continuous variables presented in the study, category boundaries can be formed and each category is clearly delimited.
(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period
There is no any relative risk presented in this case-control study therefore no translation of estimates of relative risk into absolute risk present. The results are presented in odds ratio rather than in relative risk. If there is relative risk which translated into the absolute risk, the probability or chance of an event can be known.
Report other analyses done – eg analyses of subgroups and interactions, and sensitivity analyses
The other analyses done can be found under results part of this case-control study.
Summarise key results with reference to study objectives
The summarise of key results is stated clearly in the first line of discussion part of this case-control study and is with reference to study objectives.
Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias
The limitations and potential bias are stated clearly under the discussion part of this case-control study. The direction of bias is towards living women and the magnitude of bias is kept to a minimum level.
Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence
The overall interpretation of results is given in the last paragraph of the discussion in this case-control study. Objectives of the study are not stated clearly here but the results stated here are matched with the objectives. One of the limitations is also stated clearly here. Multiplicity of analyses is not found in this case-control study. For the results from similar studies and other relevant evidence, it is stated briefly here without any statistical data from the angle of reduction in risk of contralateral breast cancer with chemotherapy, protective effect on risk of contralateral breast cancer and size of the risk reduction for primary cancer.
GeneralisabilityDiscuss the generalisability (external validity) of the study results
This case-control study is not generalizable. It is stated clearly under the discussion part of this study.
This study was funded by several institutions including the US National Institutes of Health, National Cancer Institute of Canada Breast Cancer Initiative, Canadian Genetics Disease Network, Canadian Breast Cancer Foundation, Italian Association and Foundation for Cancer Research, Utah Cancer Registry as well as the Utah Department of Health and more as affirmed in the acknowledgement in the study. However, the roles of the funders as well as the conflict of interests were not described clearly by the authors in this study.
In conclusion, we have appraised the article through all the checklist items in STROBE Statement. We acknowledged the power of the study as the authors had use computerized date to minimize recall bias. In this study, the authors had fulfilled most of the items in the STROBE checklists, however, there are still some items had not been fulfilled. Inadequate discussions of some items in the checklist should be taken into consideration as to provide a strong study.