DCIS: RECAST Trial Ductal Carcinoma In Situ: Re-Evaluating Conditions for Active Surveillance Suitability as Treatment

The goal of this trial is to see if active surveillance monitoring and hormonal therapy in patients diagnosed with ductal cell carcinoma in situ (DCIS), an early stage of breast cancer, can be an effective management of the disease.

Participants will be asked to receive control hormonal therapy or an investigational hormonal therapy treatment. Participants will be asked to return for evaluation with MRI at three months and six months. Depending on the evaluation participants will have the option to continue on the treatment. If the evaluation suggests surgery is recommended, the participant will discontinue the study treatment and will undergo surgery. In addition to the treatment and MRI evaluation, participants will be asked to provide blood sample to understand their immune status, provide saliva sample for genetic testing, provide the study with a portion of the tissue or slides generated from tissue removed during surgery performed as part of their standard of care.

The goal of this trial is to see if active surveillance monitoring and hormonal therapy in patients diagnosed with Ductal cell Carcinoma In Situ (DCIS), an early stage of breast cancer, can be an effective management of the disease. The current management of most patients with DCIS involves surgical intervention with or without radiation, similar to more aggressive breast cancers. These treatments can come with some significant health effects.The main question this study aims to answer is: to determine whether novel endocrine therapy increases the fraction of patients who will be suitable for long-term active surveillance.

Participants will be asked to take one of three investigational study medication (z-Elacestrant, Testosterone + Anastrazole, or Endoxifen) or receive control hormonal therapy (Tamoxifen or an aromatase inhibitor), depending on the treatment to which they have been randomized. Participants will be asked to return for evaluation with MRI at three months and six months. Depending on the evaluation, participants will have the option to continue on the treatment, with follow up evaluations of Mammogram and MRI at 6 month intervals. If the evaluation suggests surgery is recommended, the participant will discontinue the study treatment and will undergo surgery. In addition to the treatment and MRI evaluation, participants will be asked to:

• Provide blood sample to understand their immune status
• Provide saliva sample for genetic testing
• Provide the study with a portion of the tissue or slides generated from tissue removed during surgery performed as part of their standard of care.

Participants will be followed annually for 10 years.