A PD Study of Oral eFT508 in Subjects With Advanced TNBC and HCC

Inclusion Criteria (TNBC Cohort Only): * Women ≥18 years of age * Pathologically documented diagnosis of TNBC that is metastatic or locally advanced and unresectable * Adequate hepatic function and coagulation profile * Negative HIV, HBV and HCV Inclusion Criteria (HCC Cohort Only): * Men or Women ≥18 years of age * Histological or cytological confirmed diagnosis of HCC with Barcelona Clinic Liver Cancer Stage B or C who cannot benefit from resection, local ablation, or chemoembolization * ECOG performance status of 0 or 1 * Has at least 1 measurable lesion based on irRECIST 1.1. * Negative HIV tests Inclusion Criteria (Either Cohort): * subject agrees to undergo a pre-treatment and an on-treatment biopsy of the tumor * Completion of all previous therapy for the treatment of cancer ≥3 weeks before the start of study drug * All acute toxic effects of any prior antitumor therapy resolved to Grade ≤1 before the start of study drug * Adequate bone marrow and renal function * Life expectancy of ≥3 months Exclusion Criteria (Either Cohort): * Pregnant or breastfeeding * History of another malignancy except for the following: adequately treated local basal cell or squamous cell carcinoma of the skin; in situ cervical carcinoma; adequately treated, papillary, noninvasive bladder cancer; other adequately treated Stage 1 or 2 cancers currently in complete remission; or any other cancer that has been in complete remission for ≥2 years. * Gastrointestinal disease that may interfere with drug absorption or with interpretation of GI AEs. * Known symptomatic brain metastases requiring ≥10 mg/day of prednisolone (or its equivalent). * Significant cardiovascular disease within 6 months prior to start of study drug * Ongoing risk for bleeding due to active peptic ulcer disease or bleeding diathesis or requirement for systemic anticoagulation with unfractionated heparin, low-molecular-weight heparin or heparin fractions, or oral anticoagulants. * Evidence of an ongoing systemic bacterial, fungal, or viral infection * Has received a live vaccine within 30 days of planned start of study drug * Major surgery within 4 weeks before the start of study drug * Prior solid organ or bone marrow progenitor cell transplantation * Prior therapy with any known inhibitor of MNK1 or MNK2 * Prior high dose chemotherapy requiring stem cell rescue * History of or active autoimmune disorders or other conditions that might impair or compromise the immune system * Ongoing immunosuppressive therapy, including systemic or enteric corticosteroids * Use of a strong inhibitor or inducer of cytochrome P450 (CYP)3A4 within 7 days prior to the start of study drug or expected requirement for use of a strong CYP3A4 inhibitor or inducer during study participation * Need for proton pump inhibitors and histamine H2 blockers * Previously received investigational product in a clinical trial within 30 days or within 5 elimination half lives (whichever is longer) prior to the start of study drug, or is planning to take part in another clinical trial while participating in this study * HCC Cohort Only: Portal vein invasion at the main portal (Vp4), inferior vena cava, or cardiac involvement of HCC based on imaging.