Estrogen Receptor-Positive Breast Cancer Patient-Derived Xenografts

You may be eligible if

• 1. Men and women \> age 18 with histologically documented ER+/HER2- breast cancer or with a history of ER+/HER2- breast cancer, for whom a tumor biopsy or surgical resection is clinically indicated and will be performed as standard of care.
• Tumor specimens may be from breast (progressive or recurrent) or metastatic sites. Patients with multicentric or bilateral disease are eligible.
• 2. Patients must have disease progression during neoadjuvant therapy, recurrence after neoadjuvant or adjuvant therapy, or progression after systemic therapy for metastatic disease.
• 3. ER positivity is defined as \>10% of malignant tumor cells staining positively for ER by immunohistochemistry (IHC).
• HER2 negativity is defined as IHC 0-1+, or with a fluorescence in situ hybridization (FISH) ratio of \<1.8 if IHC is 2+ or if IHC has not been done.
• 4. Excess LIVE tumor tissue must be available from the surgically resected tumor specimen, or from 1-3 extra core needle or incisional biopsy. LIVE tumor tissue must be available within 2 hours of removal from patient (shorter time is preferable).
• 5. A recurrent or progressing breast cancer must be greater than 1 cm in greatest diameter.
• 6. Prior therapy is allowed as long as excess viable tumor tissue is available from the biopsy or surgical excision procedure.
• 7. Patients must be willing to provide 6 mL of blood, which can be obtained during a routine clinically indicated blood draw (ideally, done on the same day as the tumor biopsy/surgery).
• 8. Ability to give signed informed consent.