Pembrolizumab-Epacadostat Combination to Treat Muscle-invasive Bladder UrotheLIAl canceR: PECULIAR Study (PECULIAR)

Inclusion Criteria:

1. The participant (or legally acceptable representative if applicable) provides written informed consent for the trial
2. Male/female participants who are at least 18 years of age will be enrolled in this study.
3. A male participant must agree to use a contraception during the treatment period and for at least [120 days, corresponding to time needed to eliminate any study treatments) plus an additional 120 days (a spermatogenesis cycle) for study treatments with evidence of genotoxicity at any dose] after the last dose of study treatment and refrain from donating sperm during this period.
4. A female participant is eligible to participate if she is not pregnant, not breastfeeding, and at least one of the following conditions applies: a.) Not a woman of childbearing potential (WOCBP) or b.) A WOCBP who agrees to follow the contraceptive during the treatment period and for at least [120 days (corresponding to time needed to eliminate any study treatments) plus 30 days (a menstruation cycle) for study treatments with risk of genotoxicity] after the last dose of study treatment.
5. Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2.
6. Have adequate organ function as defined in the following table Specimens must be collected within 10 days prior to the start of study treatment.
7. Histopathologically confirmed transitional cell carcinoma. Patients with mixed histologies are required to have a dominant (i.e. 50% at least) transitional cell pattern.
8. Fit and planned for cystectomy (according to local guidelines).
9. Clinical stage T2-T3a confirmed by TURB
10. N0 M0 disease by CT (or MRI) + PET/CT (within 4 weeks of initial study treatment by RECIST v1.1).

Exclusion Criteria:

1. A WOCBP who has a positive urine pregnancy test within 72 hours prior to allocation If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required.
2. Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or with an agent directed to another stimulatory or co-inhibitory T-cell receptor (eg, CTLA-4, OX-40, CD137, IDO1).
3. Has received prior systemic anti-cancer therapy including investigational agents.
4. Has received prior radiotherapy on the bladder tumor.
5. Has received a live vaccine within 30 days prior to the first dose of study drug. Examples of live vaccines include, but are not limited to, the following: measles, mumps, rubella, varicella/zoster (chicken pox), yellow fever, rabies, Bacillus Calmette-Guérin (BCG), and typhoid vaccine. Seasonal influenza vaccines for injection are generally killed virus vaccines and are allowed; however, intranasal influenza vaccines (eg, FluMist®) are live attenuated vaccines and are not allowed.

6. Is currently participating in or has participated in a study of an investigational agent within 4 weeks prior to the first dose of study treatment.

   Note: Participants who have entered the follow-up phase of an investigational study may participate as long as it has been 4 weeks after the last dose of the previous investigational agent.

7. Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drug.

8. Has a known additional malignancy that is progressing or has required active treatment within the past 3 years.

   Note: Participants with basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or carcinoma in situ (eg, breast carcinoma, cervical cancer in situ) that have undergone potentially curative therapy are not excluded. Participants with low-risk early stage prostate cancer defined as follows are not excluded; Stage T1c or T2a with a Gleason score ≤ 6 and prostatic-specific antigen (PSA) < 10 ng/mL either treated with definitive intent or untreated in active surveillance that has been stable for the past year prior to study allocation.

9. Has severe hypersensitivity (≥Grade 3) to pembrolizumab and/or any of its excipients.
10. Has 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 (eg., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment.
11. Has a history of (non-infectious) pneumonitis that required steroids or has current pneumonitis.
12. Has an active infection requiring systemic therapy.
13. Has a known history of Human Immunodeficiency Virus (HIV).
14. Has a known history of Hepatitis B (defined as Hepatitis B surface antigen [HBsAg] reactive) or known active Hepatitis C virus (defined as HCV RNA [qualitative] is detected) infection. Note: no testing for Hepatitis B and Hepatitis C is required unless mandated by local health authority.
15. Has a known history of active TB (Bacillus Tuberculosis).
16. Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the study, interfere with the subject's participation for the full duration of the study, or is not in the best interest of the subject to participate, in the opinion of the treating investigator.
17. Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial.
18. Pregnant or breastfeeding.
19. Inability to swallow tablets or capsules