Study LCB-1801-001 is an open-label, Phase 1, dose escalation (Part A) and expansion (Part B), first-in-human clinical study of NI-1801 in patients with advanced, metastatic, or recurrent solid malignancies expressing mesothelin (MSLN). The dose escalation part (Part A) of the main study will evaluate the safety and tolerability of escalating doses of NI-1801 to determine the maximum tolerated dose (MTD) and non-tolerated toxic dose (NTD) of NI-1801. The expansion part (Part B) of the main study will further evaluate the safety and efficacy of NI-1801 administered at or below the MTD in up to 10 additional subjects in order to determine the recommended Phase 2 dose (RP2D). Treatments will be administered in 28-day cycles for up to 12 months until disease progression, unacceptable toxicity, or Investigator/patient decision to withdraw study consent. The dose escalation part (Part A) of the sub-study will evaluate the safety and tolerability of escalating doses of NI-1801 in combination with anti-PD-1 antibody. The expansion part (Part B) of the sub-study will further evaluate the safety and efficacy of NI-1801 administered in combination with anti-PD-1 antibody at or below the MTD. In the randomized cohort, the experimental arm will receive the investigational drug NI-1801 at the P2RD every two weeks in combination with weekly administration of paclitaxel (80 mg/m\^2) over 4-week cycles. The control arm will be treated with weekly paclitaxel at the same regimen representing one of the standards of care (SoC) in this population. This trial specifically targets patients with platinum-resistant ovarian cancer. This cohort will be made up of 20 evaluable patients, 10 per arm.