This study is testing a new treatment, ELA026, for people aged 18 and older with relapsed or refractory T/NK Cell Malignancies (TCMs). These are types of blood cancers that come back or do not respond to treatment. The study has two parts. In the first part, the goal is to find safe doses of ELA026 by testing it on 6 to 24 participants. Once safe doses are found, more participants will try these doses in the second part. The study includes several phases: - **Screening**: This lasts up to 28 days to see if you qualify. - **Treatment**: You could receive the drug for up to 6 cycles, each cycle lasting 28 days, and possibly more if it helps. - **Follow-up**: After treatment, there's a safety check 28 days later and survival follow-ups for up to 2 years. **Key Points** - Participation is for adults with specific blood cancers that have not responded to other treatments. - The study involves multiple visits over a long period, including up to 2 years of follow-up. - Participants must not have other treatment options and must meet specific health criteria. **Eligibility**: You must not have access to other effective treatments and should not be planning a pregnancy.