RECAST (Re-Evaluating Conditions for Active Surveillance Suitability as Treatment) for DCIS: Clinical trial in progress.

TPS624 Background: Ductal Carcinoma In Situ (DCIS) is a condition where cancerous cells are confined to the breast ducts. The standard of care is surgery, either breast conservation and radiation or mastectomy. Data from the COMET study in hormone receptor-positive (HR+) DCIS demonstrates that active surveillance (AS) is a safe alternative for initial treatment. Starting with endocrine risk-reducing therapy first may assist in identifying candidates for risk reduction vs. focal surgical removal. The RECAST (Re-Evaluating Conditions for Active Surveillance Suitability as Treatment) study re-orders the treatment, starting with endocrine risk reduction, and uses serial imaging to assess treatment response to predict who can safely proceed with AS and endocrine therapy. Imaging response markers are tested to predict the success of endocrine therapy. Several novel endocrine treatments are tested. The trial gives patients a window of opportunity to evaluate the impact of endocrine therapy based on their imaging characteristics to explore alternatives to surgery. Rather than being randomly assigned to surgery or AS, all patients start with AS and serve as their own control. Methods: Women are screened for and randomized to 1 of 4 endocrine treatments, one of which is the standard of care endocrine therapy (choice of tamoxifen, baby tamoxifen, or an aromatase inhibitor is left to patient and physician discretion); MRIs are conducted at baseline, 3 and 6 months and semiquantitative imaging determines suitability for AS. Patients on AS are eligible to continue treatment for 3 years. Follow-up consists of an MRI alternating with a mammogram every 6 months. Quality of life (QOL) is measured using PROMIS and the FACT-ES composite scores. Eligibility: All patients with a diagnosis of HR+ DCIS (any grade), defined as > 50% ER+ or PR+ on immunohistochemistry Exclusion : Presence of invasive disease, pregnancy or active breastfeeding, history of deep vein thrombosis. Patients with a solid mass on MRI must have a repeated biopsy Primary objectives: To determine whether novel endocrine therapy increases the fraction of patients who are suitable for long-term AS and how medications are tolerated compared to standard endocrine treatment Primary endpoints: QOL and fraction of patients who meet criteria for remaining on AS after 6 months based on MRI Secondary endpoints: Biomarkers of response and resistance Progress to date: RECAST activated on 01/22/2024. Currently,12 sites in the US are open to enrollment. 28 are in the process of activation. There are 22 patients accrued with 6 in screening. RECAST is an important next step in elucidating the factors that predict the success of AS and provide a framework for understanding endocrine resistance in the HR+ DCIS population. Clinical trial information: NCT06075953 .