Development of Patient Derived Xenografts (PDX) in Patients With Breast Cancer

Inclusion Criteria: * Age ≥18 years. * Diagnosis of invasive breast cancer treated with neoadjuvant systemic therapy. * Surgically resectable disease following neoadjuvant systemic treatment. * At least one of the following must be true: * Received at least 2 weeks of neoadjuvant endocrine therapy * Received at least 2 months of neoadjuvant chemotherapy with suggestion of residual disease on imaging * Began neoadjuvant chemotherapy or endocrine therapy but discontinued due to evidence of progressive disease by MRI, ultrasound, or physical examination * Provide written informed consent. * Willing to return to enrolling institution for breast cancer surgery. * Willingness to provide mandatory blood specimens for future research on breast cancer at Mayo Clinic. * Willingness to provide mandatory tissue specimens for future research on breast cancer at Mayo Clinic. * Willingness to provide mandatory tissue specimens for the generation of PDX and organoids to be used future research on breast cancer at Mayo Clinic. Exclusion Criteria: * Ineligible for surgery. * History of prior malignancy \<3 years prior to registration. Exceptions for non-melanoma skin cancer, papillary thyroid cancer, non-invasive cancer (e.g., carcinoma in situ of the cervix).