A Study of TLN-254 in Participants With Relapsed or Refractory T-cell Lymphoma

Inclusion Criteria:

Age:

1. At least 18 years of age at the time of signing the informed consent form (ICF). Type of Participant and Disease Characteristics:

2. Cohort 1: Peripheral T-cell lymphoma (PTCL) that has relapsed after, or notresponded to at least one prior systemic treatment regimen. Participants withAnaplastic large cell lymphoma (ALCL) should have received prior brentuximab vedotintreatment.

• Nodal T-follicular helper (TFH) cell lymphoma angioimmunoblastic; Follicularhelper T-cell lymphoma, angioimmunoblastic type (angioimmunoblastic T-celllymphoma).

• Nodal TFH cell lymphoma, follicular type; Follicular helper T-cell lymphoma,follicular type.

• Nodal TFH cell lymphoma, not otherwise specified (NOS); Follicular helperT-cell lymphoma, NOS.

• PTCL, NOS.

• Anaplastic large-cell lymphoma, Alkaline phosphatase (ALK) positive.

• Anaplastic large-cell lymphoma, ALK negative. Cohort 2: Relapsed/refractory CTCL which has relapsed after, or not responded to atleast two prior systemic treatments.

• Sezary syndrome

• Mycosis fungoides

3. Participant must have measurable disease at study entry.

4. Freshly biopsied or archival tissue available. Diagnostic Assessments:

5. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2.

6. Adequate organ function. Contraception:

7. Participants must accept and follow the pregnancy prevention plan.

Exclusion Criteria:

Medical Conditions:

1. Participants must not have prior systemic anti-cancer treatment less than or equalto (≤) 5 half-lives or 4 weeks, allogeneic SCT≤90 days or autologous SCT ≤60 daysprior to study intervention initiation.

2. Participants must not have any condition, including significant acute or chronicmedical illness, active or uncontrolled infection, or the presence of laboratoryabnormalities, that places participants at unacceptable risk if participating inthis study.

3. Current or past history of central nervous system (CNS) involvement.

Other Exclusions:

• Pregnant or lactating women.

• Unable to swallow tablets.