Brinton 2013a.

Methods	Retrospective cohort.
Participants	Cohort of 87,418 women who received treatment or were registered with fertility problems on or after September 25; 1994 were retrieved from a registry. Women were diagnosed as having problems conceiving, having undergone fertility treatments in either the hospital or community clinics, or having purchased medications for fertility problems. Excluded were 6 women who exited before or on the same day as entry and 9 who were diagnosed with cancer before entry into the cohort, leaving 87,403 eligible study subjects. Of these, 67,608 were exposed to fertility treatments. Mean follow‐up, 8.1 years.
Interventions	Exposure to any fertility treatment, any IVF, number of IVF cycles, clomiphene citrate, gonadotropin‐releasing hormone analogues, or progestogen.
Outcomes	Histologically confirmed endometrial cancer, retrieved from nationwide cancer registry. Medical records were also examined to assure completeness of information on malignant tumour diagnoses. Incident cases in total cohort, 41; in exposed cohort, 34.
Notes	Subfertility indication was classified into 6 non‐mutually exclusive categories: 1) male subfertility, 2) anovulation, 3) mechanical causes, 4) polycystic ovary syndrome, 5) endometriosis, and 6) pituitary‐hypothalamic problems.
Risk of bias
Bias	Authors' judgement	Support for judgement
Selection bias (comparability)	High risk	Quote: "We considered ineligible for study six women who exited before or on the same day as entry (one due to death) and nine who were diagnosed with cancer before entry into the cohort". Comment: Outcome not likely to be present at start. Quote: "Information on whether the patient had been exposed to any fertility treatment was classified according to whether she ever had IVF treatment". Comment: Non‐exposed drawn from the same population as the exposed cohort. Comment: No comparability on cause of subfertility, diabetes mellitus, polycystic ovary syndrome (PCOS), and obesity was ensured.
Selection bias (confounding)	High risk	Quote: "Adjusted for age at entry, body mass index, smoking, parity at exit, and socioeconomic status". Comment: Analyses inadequately controlling for potential confounders.
Performance bias	High risk	Quote: "From the women's electronic medical records (EMR), we attempted to obtain information on demographic factors (date of birth, district of residence, enumeration area), potential cancer risk factors (parity status at cohort entry, parity status at cohort exit, number of children at exit, weight, height, ever smoked cigarettes, and infertility indication), and fertility treatments". Comment: Exposure to ovary‐stimulation drugs was ascertained by medical records. Blindness regarding the allocated interventions not guaranteed.
Detection bias	Low risk	Quote: "After appropriate Institutional Review Board clearances, we linked our study population with the Israel Cancer Registry (ICR)". Comment: Outcome was ascertained by record linkage.
Attrition bias	Low risk	Quote: "The coverage of solid tumours in the registry is > 90% nationwide" Comment: Follow‐up was expected to be rather complete.
Selective reporting (reporting bias)	Low risk	Comment: All of the study’s prespecified (primary and secondary) outcomes that were of interest in the review have been reported in the prespecified way.
Other bias	High risk	Quote: "Mean 8.1 years of follow‐up, SD 3.8". Comment: The length of follow‐up was considered inadequate. Comment: Non‐RCT study