A Single Arm Phase II Trial of Circulating Tumor DNA-guided Adjuvant Therapy With Elacestrant in Hormone Receptor Positive HER2 Negative Breast Cancers at Risk for Late Recurrence (CATE)

This is a single-arm, phase II study examining elacestrant in the adjuvant treatment of patients with ER+ breast cancer who test positive for circulating tumor DNA (ctDNA) during the screening period of the trial. Patients with ER+ breast cancer anatomic stage IIB or III at diagnosis who are at least five years from diagnosis and have completed intended course of adjuvant endocrine therapy and are currently off endocrine therapy will be screened with ctDNA testing. Patients who test positive for ctDNA during the screening phase will receive treatment with elacestrant for one year and continue ctDNA testing and imaging with CT scans every three months. During the follow-up period, patients in the study will continue to be ctDNA tested every six months and monitored for one year and will be allowed to continue on elacestrant for an additional year, resume standard endocrine therapy, or continue with standard of care surveillance during follow up.

Inclusion Criteria:

1. Women or men aged 18 years and older.
2. Previous diagnosis of anatomic stage IIB or anatomic stage III histopathologically or cytologically confirmed ER+, HER2-, breast cancer per local laboratory as per ASCO/CAP guidelines. In the context of this trial, ER status will be considered positive if >10% of tumor cells demonstrate positive nuclear staining by immunohistochemistry, with or without progesterone receptor positivity. Patients who are PR positive but ER-negative are not eligible.
3. Participants must have been diagnosed with ER+HER2- breast cancer at least five years ago and no more than 15 years ago and must have completed adjuvant endocrine therapy.
4. Participants must be off endocrine therapy for at least six months prior to screening.

Exclusion Criteria:

1. Known current metastatic disease.
2. Known contraindication to receiving elacestrant as per FDA package insert.
3. Current treatment with endocrine therapy.
4. Prior treatment with elacestrant or other investigational SERDs.
5. Current or past invasive cancer other than breast cancer, except:
   1. Adequately treated basal or squamous cell carcinoma of the skin.
   2. Cancer survivors of previously diagnosed invasive cancer who were treated with curative intent and have no evidence of disease recurrence for five years or more and are considered low risk for future recurrence by the treating physician.
6. Patients in the screening phase, or in the randomized trial (treatment phase), cannot start receiving therapy on another therapeutic clinical trial.