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).