Drug-induced IL occurs with selpercatinib or pralsetinib treatment. The frequency increases with longer drug exposure. Serial monitoring is essential and when necessary, dose modification. Most cases do not lead to treatment discontinuation.

Oncogenic RET gene rearrangements drive a subset of lung adenocarcinomas (LUAD) and the tyrosine kinase inhibitors (TKIs) selpercatinib and pralsetinib are approved therapeutics. By contrast, upfront treatment with selpercatinib and crizotinib in orthotopic tumors yielded complete elimination of 7 of 9 TR.1 tumors and both deepened and prolonged the duration of response in TR.2 tumors. The findings provide new insight into mechanisms of acquired resistance through bypass signaling and highlight the therapeutic benefit of simultaneous upfront blockade of driver oncogenes and dominant resistance mechanisms in LUAD.

Given the current pricing, neither selpercatinib as a first-line therapy nor as a second-line therapy was deemed to be cost-effective compared with chemotherapy for advanced NSCLC patients with RET fusions. Further real-world studies of selpercatinib and development of health outcome estimate scales are needed to provide additional evidence for clinicians and health policy decision-makers.

Upon re-evaluation one year later, imaging revealed recurrent paratracheal, pulmonary, hepatic, and possible adrenal metastases, prompting re-initiation of selpercatinib at a reduced dose, which she tolerated and continues to this day with surveillance of symptoms, serial electrocardiograms, laboratory work, and imaging. This case illustrates the aggressive course of RET M918T-mutated MEN2B and underscores the importance of early genetic diagnosis, vigilant surveillance, and continuity of selective RET inhibitor therapy to optimize disease control.

These molecular changes were associated with higher cell motility of TPC-1-SelpRWT1-knockdown. Collectively, these findings suggest that WT1 is a critical regulator involved in tumor plasticity, thereby supporting selpercatinib resistance.

The therapeutic strategy involved an immediate switch from rivaroxaban to therapeutic low-molecular-weight heparin (LMWH) and the initiation of dual targeted therapy with selpercatinib and tepotinib. Upon diagnosis of NBTE, a rapid oncologic work-up is warranted, as ongoing tumor progression is highly likely. This case questions the appropriateness of direct oral anticoagulants in patients with NBTE and active, progressive malignancy.

Safety was consistent with previous ARROW reports; no hypersensitivity was reported in patients receiving prior immunotherapies. Pralsetinib produced robust, durable responses with manageable safety in treatment-naïve and previously treated patients with RET fusion-positive NSCLCs, confirming previous findings with longer follow-up.

However, QTc prolongation occurred in both of our patients, suggesting that it may represent a clinically relevant concern in selected individuals. Appropriate dose adjustment and careful monitoring may facilitate continued treatment in selected patients.

P2, N=124, Active, not recruiting, SWOG Cancer Research Network | Trial completion date: Mar 2026 --> Dec 2026 | Trial primary completion date: Mar 2026 --> Dec 2026

P3, N=291, Active, not recruiting, Loxo Oncology, Inc. | Trial completion date: Feb 2026 --> Nov 2027

P=N/A, N=0, Active, not recruiting, Eli Lilly and Company | Recruiting --> Active, not recruiting

Following the development of resistance, combination therapy with pralsetinib and anlotinib successfully achieved a partial response again. This case underscores the importance of comprehensive molecular testing across multiple lesions to guide precision therapy and provides clinical insights into RET fusion-positive lung cancer treatment and post-resistance combination strategies.