Table 2.

ROBINS‐I tool (stage 1): treatment

List of confounding domains relevant to all or most studies (prognostic factors that predict whether an individual receives a SERM/AI versus no SERM/AI)

Age Menopausal status Body mass index Hormone replacement therapy ER status Tumour size Nodal status HER‐2 status

List of cointerventions that could be different between intervention groups and that could impact on outcome

Hormone replacement therapy Anti‐HER2 therapy Chemotherapy Radiotherapy Mastectomy

ER: oestrogen receptor HER: human epidermal growth factor receptor SERM/AI: selective oestrogen receptor modulator/aromatase inhibitor