Inclusion Criteria:

          -  Provision of informed consent prior to any study-specific procedures.

          -  Female or male ≥18 years of age.

          -  Histologically or cytologically confirmed relapsed/refractory and/or metastatic breast
             cancer with the exception of human epidermal growth factor receptor 2-positive breast
             cancer.

          -  Evaluable or measurable disease as per the RECIST 1:1.

          -  Normal organ and bone marrow function measured within 28 days prior to administration
             of the study treatment.

          -  Eastern Cooperative Oncology Group performance status of 0 or 1.

          -  Life expectancy ≤6 months.

          -  Postmenopausal or evidence of non-childbearing status for women of childbearing
             potential (WOCBP): negative serum (beta-human chorionic gonadotropin) pregnancy test
             within 28 days of study treatment and confirmed prior to treatment on Day 1.

          -  WOCBP must be willing to use 2 highly effective methods of contraception for the
             course of the study through 1 month after the last treatment dose.

          -  Male patients must be willing to use condom contraception for the course of the study
             through 3 months after the last treatment dose.

          -  Willing and able to comply with the protocol for the duration of the study including
             undergoing treatment and scheduled visits and examinations.

          -  Willing to undergo biopsy as required by the study.

        Exclusion Criteria:

          -  Involvement in the planning and/or conduct of the study (applies to both AstraZeneca
             staff and/or staff at the study site).

          -  Previous allogenic bone marrow transplant or double umbilical cord blood
             transplantation.

          -  Whole blood transfusions in the last 120 days prior to study entry.

          -  Unable to swallow orally administered medication and patients with gastrointestinal
             disorders likely to interfere with absorption of the study treatment.

          -  Concomitant use of known strong or moderate cytochrome P450 (CYP)3A inhibitors.

          -  Concomitant use of known strong or moderate CYP3A inducers.

          -  Persistent toxicities (CTCAE Grade 2) caused by previous cancer therapy, excluding
             alopecia.

          -  Participants with myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML) or with
             features suggestive of MDS/AML.

          -  Known hypersensitivity to olaparib or vorinostat or any of their excipients or
             analogues (PARP/HDAC inhibitors).

          -  Breastfeeding women.

          -  No active malignancy except for non-melanoma skin cancer, in situ cervical cancer, or
             a treated cancer from which the patient has been continuously disease free for more
             than 5 years.

          -  Pneumonitis or at risk of pneumonitis.

          -  Uncontrolled brain or leptomeningeal metastases.

          -  Any systemic chemotherapy or radiation therapy within 4 weeks prior to study entry.

          -  Major surgery within 4 weeks of starting the study treatment.

          -  Participation in another clinical study with an investigational product during the
             last 3 months.

          -  Any previous treatment with PARP inhibitor including olaparib or HDAC inhibitor
             including vorinostat.

          -  New York Heart Association Class III or IV heart failure or unstable angina.

          -  History of liver disease, such as cirrhosis or active/chronic hepatitis B or C.

          -  Sustained or clinically significant cardiac arrhythmias including sustained
             ventricular tachycardia, ventricular fibrillation, clinically significant bradycardia,
             advanced heart block (Mobitz II or higher atrioventricular nodal block), prolonged
             corrected QT interval (mean >470 milliseconds), or history of acute myocardial
             infarction.

          -  Risk factors for torsades de pointes such as hypokalemia, hypomagnesemia, cardiac
             failure, clinically significant/symptomatic bradycardia, or high-grade
             atrioventricular nodal block.

          -  Concomitant disease(s) that could prolong QT interval such as autonomic neuropathy
             (caused by diabetes or Parkinson's disease), human immunodeficiency virus (HIV),
             cirrhosis, uncontrolled hypothyroidism, or cardiac failure.

          -  Concomitant medication(s) known to prolong QT interval (patient must be off the drug
             for 2 weeks to be eligible).

          -  Presence of active or suspected acute or chronic uncontrolled infection or history of
             immunocompromise, including participants who are known to be serologically positive
             for HIV.

          -  Any severe and/or uncontrolled medical conditions or other conditions that could
             affect study participation, such as severely impaired lung function; any active (acute
             or chronic) or uncontrolled infection/disorders; or non-malignant medical illnesses
             that are uncontrolled or whose control may be jeopardized by the study treatment.