Pembrolizumab/Placebo Plus Paclitaxel With or Without Bevacizumab for Platinum-resistant Recurrent Ovarian Cancer (MK-3475-B96/KEYNOTE-B96/ENGOT-ov65).

Inclusion Criteria:

• Has histologically confirmed epithelial ovarian, fallopian tube, or primaryperitoneal carcinoma.

• Has received 1 or 2 prior lines of systemic therapy for ovarian cancer (OC),including at least 1 prior platinum-based therapy. Participants may have received aprior poly (ADP-ribose) polymerase inhibitor (PARPi), anti-programmed cell death 1protein (PD-1)/anti-programmed cell death ligand 1 (PD-L1) therapy, bevacizumab, orhormonal therapy; these will not be considered a separate line of therapy. Anychemotherapy regimen change due to toxicity in the absence of disease progressionwill be considered part of the same line of therapy.

• Has provided documented informed consent for the study.

• Has radiographic evidence of disease progression within 6 months (180 days) afterthe last dose of platinum-based chemotherapy for OC (i.e., platinum-resistantdisease).

• Is a candidate for paclitaxel chemotherapy (and bevacizumab, if using).

• Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1assessed within 3 days before randomization.

• For a female participant, she is not pregnant or breastfeeding, and at least one ofthe following conditions applies: Is not a woman of childbearing potential (WOCBP)OR Is a WOCBP and uses a contraceptive method that is highly effective (with afailure rate of <1% per year).

• Has radiographically evaluable disease, either measurable or nonmeasurable perResponse Evaluation Criteria In Solid Tumors (RECIST) 1.1, as assessed by the localsite investigator.

• Archival tumor tissue sample or newly obtained core or incisional/excisional biopsyof a tumor lesion not previously irradiated has been provided.

• Have adequate organ function.

Exclusion Criteria:

• Has nonepithelial cancers, borderline tumors, mucinous, seromucinous that ispredominantly mucinous, malignant Brenner's tumor and undifferentiated carcinoma.

• Has primary platinum-refractory disease, defined as disease that has progressed perradiographic imaging while receiving or within 28 days of the last dose offirst-line platinum-based therapy.

• Has prior disease progression on weekly paclitaxel alone.

• Has received >2 prior lines of systemic therapy for OC.

• Has received prior systemic anticancer therapy including investigational agents ormaintenance therapy (including bevacizumab maintenance therapy), within 4 weeksbefore randomization.

• Has received prior radiation therapy within 2 weeks of start of study intervention.

• Has not recovered adequately from surgery and/or any complications from the surgery.

• Has received colony-stimulating factors (e.g., granulocyte colony-stimulating factor [G-CSF], granulocyte-macrophage colony-stimulating factor,[GM-CSF] or recombinanterythropoietin) within 4 weeks before randomization.

• Has received a live or live-attenuated vaccine within 30 days before the first doseof study intervention.

• Has received investigational agent or has used an investigational device within 4weeks prior to study intervention.

• Has a diagnosis of immunodeficiency or is receiving chronic systemic steroidtherapy.

• Has a known additional malignancy that is progressing or has required activetreatment within the past 3 years.

• Has known active central nervous system (CNS) metastases and/or carcinomatousmeningitis.

• Has severe hypersensitivity (≥Grade 3) to pembrolizumab, paclitaxel, or bevacizumab (if using) and/or any of their excipients.

• Has an active autoimmune disease that has required systemic treatment in the past 2years.

• Has a history of (noninfectious) pneumonitis/interstitial lung disease that requiredsteroids or has current pneumonitis/interstitial lung disease.

• Has an active infection requiring systemic therapy.

• Has a known history of human immunodeficiency virus (HIV) infection.

• Has a known history of Hepatitis B or known active Hepatitis C virus infection.

• Has a history or current evidence of any condition, therapy, laboratory abnormality,or other circumstance that might confound the results of the study.

• Has a known psychiatric or substance abuse disorder that would interfere with theparticipant's ability to cooperate with the requirements of the study.

• Participant, in the judgement of the investigator, is unlikely to comply with thestudy procedures, restrictions, and requirements of the study.

• Has had an allogenic tissue/solid organ transplant.

For bevacizumab treatment

• Has uncontrolled hypertension.

• Has current, clinically relevant bowel obstruction including related to underlyingepithelial OC, abdominal fistula or gastrointestinal perforation, intra-abdominalabscess, or evidence of rectosigmoid involvement by pelvic exam.

• Has a history of thrombotic disorders, hemorrhage, hemoptysis, or activegastrointestinal bleeding within 6 months before randomization.