DNA-guided Second Line Adjuvant Therapy for High Residual Risk, Estrogen Receptor Positive, HER-2 Negative Breast Cancer (DARE)

Required: ESR1 expression >=10% (>=10% ER positivity by immunohistochemistry)

ER positivity is defined as equal to or greater than 10% ER positivity by immunohistochemistry, regardless of progesterone receptor (PR) status.

Required: HER2 (ERBB2) wild-type

HER-2 negative

Must have received: endocrine therapy (aromatase inhibitor, tamoxifen) — adjuvant

Patients may have completed adjuvant endocrine therapy and are within 7 years since the date of their definitive breast surgery, or may be currently taking an aromatase inhibitor, or tamoxifen, as adjuvant endocrine therapy and have completed at least 6 months (i.e. 24 weeks), but no more than 7 years of endocrine therapy.

Cannot have received: fulvestrant (fulvestrant)

Prior or current treatment with fulvestrant

Cannot have received: CDK4/6 inhibitor

Exception: allowed if last treatment was 12 or more months ago

current treatment with a CDK4/6 inhibitor, or treatment in the prior 12 months