(i) determining that the subject has an MGIN+ score above an MGIN+ score cut point by:

assaying or having assayed a sample of breast cancer cells from the subject for the expression levels of BUB1B, CENPA, NEK2, RACGAP1 and RRM2;

summing or having summed the expression levels of BUB1B, CENPA, NEK2, RACGAP1 and RRM2 as a single index into a subject's MGI index;

determining or having determined one or more clinicopathological factor selected from tumor size and grade of the subject's breast cancer;

calculating or having calculated the MGIN+ score of the subject by combining the subject's MGI index with the one or more clinicopathological factor of the subject using a multivariate Cox-proportional model;

comparing or having compared the subject's MGIN+ score to the MGIN+ score cut point, wherein the MGIN+ score cut point has been pre-determined based on the MGIN+ scores calculated for a training set of samples containing breast cancer tissues from patients who had breast cancer recurrence and patients who did not have breast cancer recurrence; and

(ii) treating the subject with an MGIN+ score above the MGIN+ cut point with chemotherapy or endocrine therapy.