• Female participant is at least 18 years of age (at the time of informed consent).

• Participant has:

• i. histologically or cytologically proven Stage 1, FIGO grade 1 or 2, MMR deficient (Absence of at least one MMR protein (MLH1, PMS2, MSH2, MSH6) by immunohistochemistry.) endometrioid endometrial adenocarcinoma, and

• ii. wish to preserve the uterus or are not a suitable candidate for hysterectomy.

• Participant has an ECOG performance status of ≤ 2

• Participant demonstrates no evidence of extrauterine disease assessed from all available clinical evidence (physical examination findings) and medical imaging including standard of care diagnostic CT, MRI, ultrasound, or X-ray and screening gadolinium contrast pelvic MRI

• Participants must have adequate organ and bone marrow function defined as:

• i. absolute neutrophil count 1.5 x 109/L ii. platelets 100 x 109/L iii. haemoglobin ≥9 g/dL

• Adequate liver function:

• iv. total bilirubin \< 1.5x institutional upper limit normal (ULN) v. AST/ALT \< 2. 5 - 3x ULN

• Adequate renal function as defined by:

• vi. Creatinine \< 1.5x institutional upper limits OR creatinine clearance \> 30 ml/min

• Adequate coagulation profile:

• vii. INR or PT ≤ 1.5 x ULN unless the participant is receiving anticoagulant therapy as long as INR or PTT is within the therapeutic range of intended use of anticoagulants viii. aPTT ≤ 1.5 x ULN unless the patient is receiving anticoagulant therapy as long as INR or PTT is within the therapeutic range of intended use of anticoagulant

• A potential participant with a clinical abnormality or laboratory parameters outside the normal reference range for the population being studied may be rescreened once, at the Investigator's discretion, and may be included only if the Investigator considers that the finding is unlikely to introduce additional risk factors to the participant and will not interfere with the study procedures.

• Women of child-bearing potential (WOCBP) must have a negative serum pregnancy test at enrolment prior to each treatment cycle and use a highly effective contraceptive method including; oral contraceptive pills \[OCPs\], or an intrauterine hormone device \[IUD\]) from screening until at least 4 months following the last dose of dostarlimab. Females who are abstinent from heterosexual intercourse as part of their usual lifestyle do not need to use contraception.

• Post-menopausal females. Post-menopausal status will be confirmed through testing of follicle-stimulating hormone (FSH) levels (≥ 40 IU/mL) at screening for amenorrhoeic (≥ 12 months) female participants.

• Participants with confirmed Type I or Type II diabetes mellitus must be well controlled by medication and/or diet and have glycated haemoglobin (HBAc1) \< 8.5% at screening and be willing to monitor blood glucose levels at home during study participation.

⁃ Participants must have normal blood pressure (BP) or adequately treated and controlled hypertension.

⁃ Participant is able to provide written informed consent and are willing to participate for the duration of the study and to follow study procedures.