Treatments and/or Procedures

Study Criteria

Inclusion Criteria:

  -  Participant is at least 18 years of age.

  -  Participant has proven recurrent or advanced solid tumor and has disease progression
     after treatment with available anti cancer therapies, or is intolerant to treatment
     that meets the following requirements for the part of the study they will participate
     in:

  -  a. Part 1: Any histologically or cytologically proven recurrent advanced solid tumor

  -  b. Part 2A: : Any histologically or cytologically proven recurrent advanced solid
     tumor

  -  c. Part 2B: Histologically of cytologically proven recurrent or advanced solid tumor
     with measurable lesion(s) per RECIST version 1.1 and meets one of the following
     disease types:

  -  The criteria below should be met for participant participating in:

  -  Cohort A1 (dMMR/MSI-H endometrial cancer) and

  -  Cohort A2 (MMR-proficient/MSS endometrial cancer)

  -  Participants who have progressed on or after platinum doublet therapy

  -  Participants have received no more than 2 lines of anti-cancer therapy for recurrent
     or advanced (>=Stage IIIB) disease. Prior treatment with hormone therapies is
     acceptable and does not count towards the number of anti-cancer therapies noted in the
     criterion above for this cohort.

  -  All endometrial cancer histologies are allowed except endometrial sarcoma (including
     carcinosarcoma).

  -  Participants must submit 2 scans demonstrating increase in tumor measurement that meet
     criteria for PD on or after the latest systemic anti-cancer therapy based on RECIST
     1.1 to Central Radiology prior to the first dose of dostarlimab.

  -  Presence of at least 1 measurable lesion on Baseline scan will be confirmed by central
     radiology review.

  -  Status of tumor MMR/MSI: Participants can be screened based on local MMR/MSI testing
     results using immunohistochemistry (IHC), polymerase chain reaction (PCR), or next
     generation sequencing (NGS) performed in a certified local laboratory, but participant
     eligibility needs to be determined by MMR IHC results. For participant with available
     local MMR IHC results for the respective cohort(s), tumor samples have to be submitted
     to a central IHC laboratory and its quality has to be checked and cleared prior to
     Cycle 1 Day 1 (C1D1). For participants without available local MMR IHC test results
     (participants with local PCR or NGS test results), central IHC results have to confirm
     eligibility prior to proceeding with other screening procedures. After the central IHC
     test is completed, remaining tumor tissue may be tested for further exploratory
     biomarkers or may be sent to a central NGS laboratory for further testing.

  -  Cohort E - Participants with NSCLC who progressed after at least 1 prior
     platinum-based systemic chemotherapy regimen for recurrent or advanced disease.

  -  Chemotherapy regimen in the adjuvant or neoadjuvant setting following surgery and/or
     radiation is acceptable if recurrent or advanced disease develops within 6 months from
     completion of therapy.

  -  Participants with a known epidermal growth factor receptor (EGFR) mutation must have
     received a chemotherapy regimen and an EGFR tyrosine-kinase inhibitor (TKI) (e.g.,
     erlotinib, gefitinib, afatinib, or experimental)

  -  Participants with a known anaplastic lymphoma kinase (ALK) translocation must have
     received a chemotherapy regimen and an ALK inhibitor (e.g., crizotinib, ceritinib or
     experimental)

  -  Cohort F - Participants with recurrent or advanced dMMR/MSI-H solid tumors or POLE-mut
     solid tumors, except endometrial cancers, that have progressed following up to 2 prior
     lines of systemic therapy for recurrent or advanced (>=Stage IIIB) disease and who
     have no alternative treatment options. Prior treatment with hormone therapies alone
     given for recurrent or advanced disease is acceptable and does not count towards the
     number of anti-cancer therapies.

  -  dMMR/MSI-H colorectal cancer (CRC) participants must have progressed after or been
     intolerant to treatment with fluoropyrimidine, oxaliplatin, and irinotecan.
     Progression following up to 3 prior lines of therapy is allowed.

  -  Ovarian cancer participants with platinum-resistant disease (i.e., progression
     occurred <6 months on or after platinum doublet chemotherapy): receipt of up to 1 line
     of systemic therapy after becoming platinum-resistant is allowed.

  -  Participants must submit 2 scans demonstrating increase in tumor measurement that meet
     criteria for PD based on RECIST 1.1 to Central Radiology prior to the first dose of
     dostarlimab.

  -  Tumor MMR/MSI or POLE status: Participants can be screened based on local MMR/MSI
     testing results using immunohistochemistry (IHC), polymerase chain reaction (PCR), or
     next generation sequencing (NGS) performed in a certified local laboratory, but
     participant eligibility needs to be determined by MMR IHC results. For participants
     with available local MMR IHC results for the respective cohort(s), tumor samples have
     to be submitted to a central IHC laboratory and its quality has to be checked and
     cleared prior to C1D1. For participants without available local MMR IHC test results
     (participants with local PCR or NGS test results), central IHC results have to confirm
     eligibility prior to proceeding with other screening procedures. After the central IHC
     test is completed, remaining tumor tissue may be tested for further exploratory
     biomarkers or may be sent to a central NGS laboratory for further testing.

  -  Participants who are considered for the study based on POLE mutation must have the
     local results available showing tumor mutation(s) in the exonuclease domain of the
     POLE gene (amino acid residues 268-471) to begin screening. Participants must have the
     quality of submitted tumor samples checked and cleared by a central IHC laboratory
     prior to receiving study treatment.

  -  Cohort G: Participants must have recurrent high-grade serous, endometrioid, or clear
     cell ovarian, fallopian tube, or primary peritoneal cancer.

  -  Participants must have presence of at least 1 measurable lesion on Baseline scan that
     will be confirmed by central radiology review.

  -  Participants must be considered resistant to the last administered platinum therapy,
     that is, the time from the last administered platinum dose until the initial
     documented progression (as evidenced by radiographic progression per RECIST) must be
     less than 6 months.

  -  Participants must have completed at least 1 but no more than 3 prior lines of therapy
     for advanced or metastatic ovarian cancer. Neoadjuvant, adjuvant, and the combination
     of both will be considered as 1 line of therapy. Treatment with single-agent
     bevacizumab given as maintenance is not counted as a separate line of therapy. If a
     therapeutic regimen is modified or changed for a reason other than lack of response or
     PD (such as allergic reaction, toxicity, or drug availability), this is not counted as
     a separate line of therapy. The use of single-agent hormonal therapy given for reasons
     other than PD per RECIST v1.1 (i.e., hormonal therapy given for increasing Cancer
     antigen [CA]-125 levels) is not counted as a separate line of therapy.

  -  Participants must have been previously treated with platinum-based regimen, taxane
     agent(s), and bevacizumab (bevacizumab could be used as a single agent or in
     combination with another agent, in frontline therapy, as maintenance, or for treatment
     of recurrent disease).

  -  Part 2B: Participants must have archival tumor tissue available that is formalin-fixed
     and paraffin-embedded.

  -  For participants who do not have archival tissue, a new biopsy must be performed to
     obtain a tissue sample prior to study treatment initiation. For participants without
     available archival tissue, the biopsy should be taken from the tumor lesions (either
     primary or metastatic) that have easy accessibility and low biopsy-associated risks
     and will exclude biopsies of the liver, brain, lung/mediastinum, pancreas, or
     endoscopic procedures extending beyond the esophagus, stomach or bowel.

  -  For Cohort G, participant must provide formalin fixed paraffin embedded (FFPE) tumor
     tissue block(s) with sufficient tumor content (as confirmed by the Sponsor's
     designated central laboratory) during screening to enable, for example, measures of
     homologous recombination pathway defects and PD-L1 status. The use of slides created
     from paraffin-embedded tissue as opposed to FFPE blocks must be approved by the
     Sponsor.

  -  Female participants must have a negative serum pregnancy test within 72 hours prior to
     the date of the first dose of study medication: unless they are of non-child bearing
     potential.

  -  Non child bearing potential is defined as: >= 45 years of age and has not had menses
     for > 1 year; Amenorrheic for < 2 years without a hysterectomy and oophorectomy and
     have a follicle- stimulating hormone (FSH) value in the postmenopausal range upon
     pre-study (screening) evaluation. Post-hysterectomy, post-bilateral oophorectomy, or
     post-tubal ligation. Documented hysterectomy or oophorectomy must be confirmed with
     medical records of the actual procedure or confirmed by an ultrasound, magnetic
     resonance imaging (MRI) or computed tomography (CT) scan. Tubal ligation must be
     confirmed with medical records of the actual procedure.

  -  Female participants of childbearing potential must agree to use 1 highly effective
     form of contraception with their partner starting with the screening visit through 150
     days after the last dose of study therapy.

  -  Participant has an Eastern Cooperative Oncology Group (ECOG) performance status of <=
     2 for Part 1 and <= 1 for Part 2.

  -  Participant has an adequate organ function.

Exclusion Criteria

  -  Participant has received prior therapy with an anti- programmed death receptor 1
     (anti-PD-1), anti-PD-1- ligand-1 (anti-PD-L1), or anti-PD-1 ligand-2 (anti-PD- L2)
     agent.

  -  Participant has a known uncontrolled central nervous system (CNS) metastases and/or
     carcinomatous meningitis.

  -  Participant has a known additional malignancy that progressed or required active
     treatment within the last 2 years. Exceptions include basal cell carcinoma of the
     skin, squamous cell cancer (SqCC) of the skin that has undergone potentially curative
     therapy, or in situ cervical cancer.

  -  Participant is considered a poor medical risk due to a serious, uncontrolled medical
     disorder, nonmalignant systemic disease or active infection requiring systemic
     therapy. Specific examples include, but are not limited to, active, non-infectious
     pneumonitis; uncontrolled ventricular arrhythmia; recent (within 90 days) myocardial
     infarction; uncontrolled major seizure disorder; unstable spinal cord compression;
     superior vena cava syndrome; or any psychiatric or substance abuse disorders that
     would interfere with cooperation with the requirements of the study (including
     obtaining informed consent).

  -  Participant is pregnant or breastfeeding, or expecting to conceive children within the
     projected duration of the study, starting with the Screening Visit through 150 days
     after the last dose of study treatment.

  -  Participant has a diagnosis of immunodeficiency or is receiving systemic steroid
     therapy or any other form of immunosuppressive therapy within 7 days prior to the
     first dose of study treatment.

  -  Participant has a known history of human immunodeficiency virus (HIV) (HIV 1/2
     antibodies).

  -  Participant has a known active hepatitis B (eg, hepatitis B surface antigen [HBsAg]
     reactive) or hepatitis C (eg, hepatitis C virus ribonucleic acid (HCV RNA)
     (qualitative) is detected).

  -  Participant has an active autoimmune disease that has required systemic treatment in
     the past 2 years (i.e., with use of disease- modifying agents, corticosteroids, or
     immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or
     physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency,
     etc.) is not considered a form of systemic treatment. Use of inhaled steroids, local
     injection of steroids, and steroid eye drops are allowed.

  -  Participant has as history of interstitial lung disease.

  -  Participant has not recovered (i.e., to <= Grade 1 or to Baseline) from radiation- and
     chemotherapy-induced AEs or received transfusion of blood products (including
     platelets or red blood cells) or administration of colony-stimulating factors
     (including granulocyte-colony stimulating factor [G-CSF], granulocyte macrophage
     colony-stimulating factor [GM-CSF] or recombinant erythropoietin) within 3 weeks prior
     to the first dose of study drug.

  -  Participant has participated in a study of an investigational agent and received study
     therapy or used an investigational device within 4 weeks prior to the first dose of
     study drug.

  -  Participant has received prior anti-cancer therapy (chemotherapy, targeted therapies,
     radiotherapy, or immunotherapy) within 21 days, or less than 5 times the half-life of
     the most recent therapy prior to study Day 1, whichever is shorter.

  -  Participant has not recovered adequately (<= Grade 1) from AEs and/or complications
     from any major surgery prior to starting therapy.

  -  Participant has received a live vaccine within 14 days of planned start of study
     therapy.

  -  Participant has a known hypersensitivity to dostarlimab components or excipients.

  -  For Cohort G, participants will not be eligible if they meet the following criteria:

  -  Participants who experienced disease progression within 3 months (as evidenced by
     radiographic progression per RECIST) of first-line platinum therapy.

  -  Participants with known deleterious or suspicious deleterious mutation in BRCA1 or
     BRCA2 genes (local testing permitted).

  -  Participants has received prior therapy with a poly(adenosine diphosphate-ribose)
     polymerase (PARP)-1/PARP-2 inhibitor.

  -  Participant has a history or current evidence of any condition, therapy, or laboratory
     abnormality that might confound the results of the study, might interfere with the
     participant's participation for the full duration of the study treatment, or is not in
     the best interest of the participant to participate.

  -  Participant is immunocompromised. Participants with splenectomy are allowed.