PMC10232990_01
Radiologic response to neoadjuvant selpercatinib. Computed tomography (CT) imaging of chest before and after neoadjuvant selpercatinib treatment is shown. (A) A baseline CT of the chest before selpercatinib initiation revealed a left lung mass measuring 3.1 cm (arrow). (B) A follow-up CT of the chest after 8 weeks of selpercatinib showed disease regression to 2.9 cm in the same mass (arrow). This was classified as stable disease by RECIST v1.1 per investigator assessment. RECIST, Response Evaluation Criteria in Solid Tumors.
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Baseline radiologic tumor assessments identified a left upper lobe tumor (3.1 cm,  Figure 2 ) and no evidence of lymph node or distant metastasis; no F-fluorodeoxyglucose avidity was observed. After the completion of neoadjuvant selpercatinib, the tumor decreased from 3.1 to 2.9 cm (Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 stable disease, investigator assessment,  Figure 2 ).
Pathologic response to neoadjuvant selpercatinib. Tumor specimens before and after neoadjuvant selpercatinib treatment are shown. (A) Pathologic assessment of a bronchoscopic biopsy with H&E staining before selpercatinib treatment identified a lung adenocarcinoma (x400). (B) Resected tumor after 8 weeks of selpercatinib treatment showed no evidence of viable tumor cells (x200). Reactive pneumocyte proliferation is denoted by an arrow. Cytogenetic testing of this specimen via RET FISH was negative for a RET fusion. FISH, fluorescence in situ hybridization.
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A transbronchial tumor biopsy showed adenocarcinoma of the lung ( Figure 3 ). The consensus was atypical cells represented a reactive pneumocyte proliferation (instead of carcinoma) secondary to treatment effect ( Figure 3 ).