Patient description: The patient is a 42 year-old postmenopausal woman who had a screening sonogram which revealed an abnormality in the right breast. She had no palpable masses on breast exam. Core biopsy was done and revealed a 1.8 cm infiltrating ductal breast carcinoma in the left upper outer quadrant. Lumpectomy was done and the surgical margins were clear. The tumor was HER2-positive and ER/PR negative. Axillary sampling revealed 1 positive lymph node out of 12 sampled. CXR was unremarkable. She is using “well women” multivitamins daily and no other medication. She smokes frequently and consumes alcohol occasionally. She is in a relation with only one partner and has a history of 3 pregnancies and live births. She breastfed all three children.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Anatomic Stage I Breast Cancer AJCC v8 Anatomic Stage IA Breast Cancer AJCC v8 Anatomic Stage IB Breast Cancer AJCC v8 Anatomic Stage II Breast Cancer AJCC v8 Anatomic Stage IIA Breast Cancer AJCC v8 Anatomic Stage IIB Breast Cancer AJCC v8 Anatomic Stage III Breast Cancer AJCC v8 Anatomic Stage IIIA Breast Cancer AJCC v8 Anatomic Stage IIIB Breast Cancer AJCC v8 Anatomic Stage IIIC Breast Cancer AJCC v8 Breast Ductal Carcinoma In Situ Breast Fibrocystic Change Breast Lobular Carcinoma In Situ Invasive Breast Carcinoma Prognostic Stage I Breast Cancer AJCC v8 Prognostic Stage IA Breast Cancer AJCC v8 Prognostic Stage IB Breast Cancer AJCC v8 Prognostic Stage II Breast Cancer AJCC v8 Prognostic Stage IIA Breast Cancer AJCC v8 Prognostic Stage IIB Breast Cancer AJCC v8 Prognostic Stage III Breast Cancer AJCC v8 Prognostic Stage IIIA Breast Cancer AJCC v8 Prognostic Stage IIIB Breast Cancer AJCC v8 Prognostic Stage IIIC Breast Cancer AJCC v8 Triple-Negative Breast Carcinoma PRE-REGISTRATION: Clinical T1-4, N0-3, M0 breast cancer at diagnosis (prior to the start of neoadjuvant chemotherapy) by American Joint Committee on Cancer (AJCC) staging version 8 Note: Benign breast disease, lobular carcinoma in situ (LCIS) or ductal carcinoma in situ (DCIS) in the contralateral breast is allowed Note: Contralateral invasive breast cancer is allowed if disease is of clinically lower stage, and the higher stage lesion will be the study lesion for all biopsies and tissue samples PRE-REGISTRATION: Histological confirmation of triple negative invasive breast cancer (defined as estrogen receptor [ER] =< 10%, progesterone receptor [PR] =< 10% and HER2 not amplified by in situ hybridization [ISH] or immunohistochemistry [IHC] 0/1) at diagnosis PRE-REGISTRATION: Neoadjuvant chemotherapy (NAC) with one of the following regimens that was not discontinued early due to intolerability with less than 50% of planned treatment given due to disease progression or patient request Paclitaxel or docetaxel followed by one of the following: the combination of doxorubicin and cyclophosphamide (AC); the combination of epirubicin and cyclophosphamide (EC) or the combination of 5-fluorouracil, epirubicin and cyclophosphamide (FEC) Note: Carboplatin may be added to these regimens AC or EC or FEC followed by docetaxel or paclitaxel Note: Carboplatin may be added to these regimens Docetaxel in combination with doxorubicin and cyclophosphamide (TAC)  PRE-REGISTRATION: History of deep venous thrombosis (DVT) or pulmonary embolisms (PE) =< 12 months prior to preregistration; OR Active DVT and/or PE requiring anti-coagulant therapy NOTE: Patients who are on anti-coagulant therapy for maintenance are eligible as long as the DVT and/or PE was > 12 months prior to enrollment and there is no evidence for active thrombosis (either DVT or PE) NOTE: Patients on anticoagulation are eligible; however peri-biopsy and peri-surgical management of anticoagulation is per the institutional standard of care PRE-REGISTRATION: Prior treatment with CDK 4/6 inhibitors (e.g. palbociclib, ribociclib, abemaciclib, etc.) PRE-REGISTRATION: Prior treatment with immunotherapy or radiation for this breast cancer PRE-REGISTRATION: Prior incisional or excisional breast biopsy for this cancer PRE-REGISTRATION: Any contraindications to pre-registration biopsy (such as bleeding diatheses, etc.) PRE-REGISTRATION: Receiving any investigational agent which would be considered as a treatment for the primary neoplasm PRE-REGISTRATION: Other active malignancy =< 5 years prior to registration Non-melanotic skin cancer or carcinoma-in-situ of the cervix