Study of E7386 in Participants With Selected Advanced Neoplasms

This study will be conducted to assess the safety/tolerability profile of E7386 as a single agent administered orally in participants with selected advanced or recurrent neoplasms and to determine the maximum tolerated dose (MTD) and/or recommended Phase 2 dose (RP2D) of E7386.

Inclusion Criteria: * Age greater than or equal to (\>=) 18 years * Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1 * Life expectancy \>=12 weeks * Participant must have any of the following tumor types, confirmed by available histology or cytology records or current biopsy, that is advanced, nonresectable, recurrent since last antitumor therapy, in need of systemic treatment, and for which no alternative standard therapy exists: * Dose Escalation Part: Desmoid tumors, anaplastic thyroid cancer (ATC), endometrial cancer, melanoma, colorectal carcinoma (CRC), hepatocellular carcinoma (HCC), pancreatic cancer, prostate cancer, ovarian cancer, and head and neck cancer. Enrollment of additional tumor types will be discussed with the Sponsor and agreed on a case by case basis * Dose Expansion Part: HCC with CTNNB1 mutations as detected either in tumor tissue or circulating tumor DNA (ctDNA) by Sponsor-approved assay. HCC participants must have: i. Confirmed diagnosis of HCC ii. Barcelona Clinical Liver Cancer (BCLC) Stage C disease, or BCLC Stage B disease not amenable to local therapy. * Participants must have accessible tumors to take biopsies from a pre-designated non target lesion for performance of correlative tissue studies. If the participant has only 1 measurable lesion and no other accessible lesion, the participant can be enrolled without a biopsy upon approval by the Sponsor * Measurable disease meeting the following criteria: * At least 1 lesion of \>=1.0 centimeter (cm) in the longest diameter for a non-lymph node or \>=1.5 cm in the short-axis diameter for a lymph node that is serially measurable according to RECIST 1.1 using computerized tomography/magnetic resonance imaging (CT/MRI) * Lesions that have had external beam radiotherapy (EBRT) or loco-regional therapies such as radiofrequency (RF) ablation must show evidence of progressive disease based on RECIST 1.1 to be deemed a target lesion * Adequate renal function defined as serum creatinine less than or equal to (\) 1.5\*ULN, the calculated creatinine clearance \>=30 milliliter per minute (mL/min) per the Cockcroft Gault formula (creatinine clearance \>=40 mL/min for participants with HCC) is acceptable * Adequate bone marrow function: * Absolute neutrophil count (ANC) \>=1500/millimeters cubed (mm\^3) (\>=1.5\*10\^3/microliters \[µl\]) * Platelets \>=100,000/mm\^3 (\>=100\*10\^9/Liters \[L\]) (platelets \>=75\*10\^9/L for participants with HCC) * Hemoglobin \>=9.0 grams per deciliter (g/dL) * Adequate liver function: * Total bilirubin \