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case_images: Histopathological findings of the surgical specimen. (a-c) Bronchoscopic biopsy of the left upper lobe revealing adenocarcinoma cells with mucus production. (d-f) Surgical specimen of the left upper lobe that had re-enlarged after 47 months of osimertinib treatment revealing the same adenocarcinoma cells as those identified at the initial diagnosis, as well as giant and spindle cells that were not present at the initial diagnosis. Hematoxylin and eosin staining: Original magnification 200x (a, d). Thyroid transcription factor-1 immunohistochemical staining: Original magnification 200x (b, e). Vimentin immunohistochemical staining: Original magnification 200x (c, f).
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case_images: Transbronchial biopsy of the LUL mass revealed adenocarcinoma cells, with immunohistochemistry showing thyroid transcription factor-1 (TTF-1) positivity and partial positivity for vimentin (Figure 1a-c). Histological examination revealed the presence of giant and spindle cells and the adenocarcinoma cells identified at the initial diagnosis (Figure 1d). In PC areas (Figure 1e,f), TTF-1 expression was decreased, and vimentin expression was increased, suggesting that the lung cancer had undergone histological transformation from adenocarcinoma to PC.
case_images: Imaging studies of the patient at the time of diagnosis. (a) Positron emission tomography/computed tomography revealed a 44-mm nodular shadow in the left upper lobe and left pleural thickening, with accumulation in the same area. (b) Head magnetic resonance imaging at the time of diagnosis revealing brain metastases in the left temporal lobe.
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case_images: Moreover, head magnetic resonance imaging revealed left temporal lobe brain metastases, and fluorodeoxyglucose positron emission tomography (PET)-CT showed significant accumulation in the pleural mass and the LUL of the lung (Figure 2).
case_images: Positron emission tomography/computed tomography images (a) before osimertinib treatment, (b) 42 months after osimertinib treatment, (c) 46 months after osimertinib treatment, and (d) 56 months after osimertinib treatment (9 months after surgery).
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case_images: Therefore, treatment with osimertinib was initiated after gamma-knife treatment for the brain metastases, resulting in tumor regression in the LUL of the lung and decreased pleural effusion, which was considered a partial response (Figure 3). However, 46 months after starting osimertinib treatment, the primary tumor showed re-enlargement and enhancement upon fluorodexyglucose-PET/CT (Figure 3) but no other metastatic sites.