Background: Oncogenic neuregulin 1 (NRG1) gene fusions occur in ̃0.2% of solid tumors overall and in up to 31% of cases of invasive mucinous lung adenocarcinoma [Laskin et al. Ann Oncol. 2020;31(12):1693–1703; Cadranel et al. Oncologist. 2021;26(1):7–16]. NRG1 fusion proteins provide an extracellular anchor for the epidermal growth factor (EGF) domain of NRG1 to bind to ErbB3 (HER3), leading to HER3 heterodimerization and activation of downstream signaling pathways, resulting in oncogenesis. Afatinib, an irreversible pan-ErbB tyrosine kinase inhibitor, represents a potential treatment for NRG1-fusion positive (NRG1+) tumors. This study aims to examine the safety and efficacy of afatinib in patients with NRG1+ solid tumors, for which no authorized targeted therapy exists. Methods: This prospective, decentralized, US study (NCT05107193) will include 40 evaluable patients aged ≥18 years. Participating molecular test providers across the USA will identify eligible fusions in the course of routine diagnostic assays. When a patient with an NRG1 fusion is identified, participating test providers will notify the treating physician of the study as a treatment option for the patient. Patients’ primary oncologists will then contact the trial sponsor to confirm patient eligibility. Once approved by the central Institutional Review Board, patients will receive afatinib on a single-patient protocol basis, until disease progression or treatment is no longer tolerated. The recommended dosage per SmPC is 40 mg orally QD. Patients will be screened and enrolled into the study at their existing point-of-care setting. Inclusion criteria include a histologically or cytologically confirmed diagnosis of an advanced, unresectable/metastatic, non-hematologic malignancy with an NRG1 fusion, evaluable per RECIST 1.1. Any coding gene as the NRG1 fusion partner is permitted. Fusion status will be confirmed prospectively by a contracted molecular test provider. Exclusion criteria include prior systemic anti-cancer therapy or investigational drug within 14 days or 5 half-lives (whichever is shorter) of the start of afatinib treatment; an actionable driver mutation other than NRG1 fusion for which FDA-approved targeted therapy is available; and prior treatment with an ErbB-targeted therapy. The primary endpoint of the study is confirmed objective response (OR) by independent central review per RECIST 1.1, defined as best overall response of either complete response or partial response and analysed as the proportion of patients with an OR. The key secondary endpoint is duration of response, defined as the time from the first documented OR to progression or death. Secondary endpoints include time to OR and disease control per investigator assessment. Safety will also be assessed. The study is open for recruitment. Clinical trial information: NCT05107193.