Inclusion Criteria:

- Patients must be ≥ 18 years of age.

- Female patients with histologically diagnosed relapsed high grade serous ovarian
cancer (including primary peritoneal and / or fallopian tube cancer) or high
grade endometrioid cancer.

- Documented mutation in BRCA1 or BRCA2 that is predicted to be deleterious or
suspected deleterious (known or predicted to be detrimental/lead to loss of
function).

- Patients who have received at least 2 previous lines of platinum containing
therapy prior to randomisation

For the penultimate chemotherapy course prior to enrolment on the study:

• Patient defined as platinum sensitive after this treatment; defined as disease
progression greater than 6 months after completion of their last dose of platinum
chemotherapy

For the last chemotherapy course immediately prior to randomisation on the study:

- Patients must be, in the opinion of the investigator, in response (partial or
complete radiological response), or may have no evidence of disease (if optimal
cytoreductive surgery was conducted prior to chemotherapy), and no evidence of a
rising CA-125, following completion of this chemotherapy course

- Patient must have received a platinum based chemotherapy regimen (carboplatin or
cisplatin) and have received at least 4 cycles of treatment

Exclusion Criteria:

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

- BRCA 1 and/or BRCA2 mutations that are considered to be non detrimental (e.g.,
"Variants of uncertain clinical significance" or "Variant of unknown significance" or
"Variant, favor polymorphism" or "benign polymorphism" etc.)

- Patients who have had drainage of their ascites during the final 2 cycles of their
last chemotherapy regimen prior to enrolment on the study.