A Study of a Selective ERBB2 Inhibitor (CGT4255), in Patients With Advanced Solid Tumors

This study tests a new oral targeted drug called CGT4255 for people with advanced solid tumors that have changes in a gene called ERBB2 (also known as HER2), which drives tumor growth. It tests the drug alone and potentially in combination with other treatments. **You may be eligible if...** - You have advanced, unresectable, or metastatic cancer with a documented ERBB2 mutation, HER2 overexpression, or NRG1 gene fusion (Part A: any solid tumor; Part B: non-small cell lung cancer; Part C: breast cancer) - Your cancer has measurable disease on scans - You are well enough to carry out daily activities (ECOG 0–1 for Part A; 0–2 for Parts B and C) - Your blood and organ function tests are within acceptable ranges **You may NOT be eligible if...** - You received chemotherapy or targeted therapy too recently before the study - You had major surgery (such as chest or brain surgery) within 4 weeks of starting the study - You have significant heart problems - You still have unresolved serious side effects from prior cancer treatment - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.