This is the first study to evaluate the incidence and progression of indeterminate lesions in breast cancer in an Asian population. •Most common site of occurrence of an indeterminate lesion was in the lung (60.9%).• A small but significant proportion of these indeterminate lesions will progress to metastatic disease (3.8%).• Routine biopsy of such lesions is not recommended, but dedicated imaging can be considered if resources permit.• Surveillance of such indeterminate lesions is recommended.