This is an open-label, phase 1/1b study evaluating the safety, tolerability, pharmacokinetic (what the body does to the drug), pharmacodynamic (what the drug does to the body), and antitumor activity of CGT4255 in adult participants with advanced solid tumors with ERBB2 alterations or HER2 overexpression.
Part A: Locally advanced, metastatic, and/or unresectable solid tumor with documented ERBB2-activating alteration or NRG1 gene fusion in blood and/or tumor or HER2 overexpression in tumor
Part B: Locally advanced, metastatic, and/or unresectable NSCLC with documented ERBB2 mutation in blood and/or tumor
Part C: Locally advanced, metastatic and/or unresectable breast cancer with documented ERBB2 mutation in blood and/or tumor or HER overexpression in tumor
Have measurable disease per RECIST v1.1.
Received small molecule chemotherapy or anticancer therapies or radiotherapy within certain timeframes before first dose of study drug.
Major surgeries (eg, craniotomy and thoracotomy) within 4 weeks of the first dose of study drug.
Treatment with palliative focal radiotherapy (cranial or extracranial) (eg, stereotactic radiosurgery or intensity-modulated radiation therapy) ≤2 weeks before the first dose of study drug; treatment with whole-brain radiotherapy ≤4 weeks before the first dose of study drug.
Clinically significant cardiac disease.