• Provision of informed consent prior to any study specific procedures

• Women age greater than 18 years with advanced/metastatic HER2 negative, BRCA germline positive breast cancer. Estrogen receptor positive (ER+) patients must have progressed on a prior endocrine therapy or are considered inappropriate for any FDA approved endocrine therapies for ER+ breast cancer.

• Eligible patients must agree to a mandatory fresh biopsy (excluding bone) at screening. In addition, if available, an archival tissue sample will also be collected at screening.

• Patients must have normal organ and bone marrow function measured within 28 days (baseline screening) as defined below:

‣ Hemoglobin (Hgb) \>/= 10.0 g/dL with no blood transfusion in the past 28 days prior to the administration

⁃ Absolute neutrophil count (ANC) \>/= 1.5 x 109/L with no GCSF administration within 28 days prior to administration of study treatment

⁃ Platelet count \>/= 100 x 109/L

⁃ Total bilirubin \</= 1.5 x institutional upper limit of normal (ULN)

⁃ Aspartate aminotransferase (AST) / Alanine aminotransferase (ALT) \</=3.0 x institutional upper limit of normal unless liver metastases are present in which case they must be \</=5x ULN

∙ 4\) Eastern Cooperative Oncology Group (ECOG) performance status 0-1 5) Patients must have life expectancy \>/= 16 weeks. 6) Negative urine or serum pregnancy test within 28 days of study treatment and confirmed prior to treatment on Cycle 1 day 1 and during the study for child bearing potential women.

∙ • Female subjects must either be of non-reproductive potential (ie, post-menopausal by history: ≥ 60 years old and no menses for ≥1 year without an alternative medical cause; OR history of hysterectomy, OR history of bilateral tubal ligation, OR history of bilateral oophorectomy) or must have a negative serum pregnancy test upon study entry and be using highly effective contraception (that is, methods with a failure rate of less than 1% per year) for both male and female subjects if the risk of conception exists (Note: The effects of the trial treatment on the developing human fetus are unknown; thus, women of childbearing potential and men must agree to use highly effective contraception, defined in Appendix E or as stipulated in national or local guidelines). Highly effective contraception must be used 30 days prior to first trial treatment administration, for the duration of trial treatment, and at least for 1 month after stopping trial treatment.

∙ 7\) Patients is willing and able to comply with the protocol for the duration of the study including undergoing treatment and scheduled visits and examinations. 8) Patient has measurable disease, per RECIST v 1.1. At least one lesion, not previously irradiated or biopsied for this study that can be accurately measured at baseline as \>/= 10 mm in the longest diameter (except lymph nodes which must have short axis ≥ 15 mm) with computed tomography (CT) or magnetic resonance imaging (MRI).

∙ 9\) Willingness to undergo baseline biopsy of metastatic lesion (repeat biopsy at progression/or end of the study is optional) 10) Willingness to have research blood draw at baseline and at progression/end of the study 11) Patient should have previously treated with any PARP inhibitor ((neo)adjuvant or metastatic) setting) and must have remained on treatment for \>/= 2 months prior to progression of disease.

∙ 12\) Able to swallow and retain oral medications and without gastrointestinal (GI) illnesses that would preclude absorption of Olaparib or ceralasertib.

∙ 13\) Non-english speaking subject can be enrolled