case_images: PMC10926684_01
case_images: Histopathology of the VATS biopsy of the mediastinal node. (A). Low power (20X) view of hematoxylin and eosin-stained section of 4R lymph node showing a lymph node entirely replaced by an epithelioid neoplasm with areas of dense fibrosis and fibrous bands. (B, C). High power magnification (400X) of the tumor showing relatively uniform tumor cells with abundant dense eosinophilic cytoplasm and round to oval nuclei some that are located at one side of the cells (plasmacytoid appearance). The nuclei have fine chromatin and no or small nucleoli. (D, E). Immunostains for cytokeratin (200X) and calcitonin (400X) are diffusely positive in the tumor cells. (F). An immunostain for PAX-8 (400X) is negative.
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case_images: TTF1, and PAX-8 ( Figure 1 ). The differential diagnosis included MTC or metastatic atypical carcinoid tumor.
case_images: The CT of chest demonstrates extensive bilateral hilar and mediastinal lymphadenopathy (white arrows). Bilateral pleural effusion and moderate pericardial effusion are noted (black arrows). The visualized portion of the thyroid gland is normal.
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case_images: The CT chest revealed marked worsening with the enlargement of mediastinal, hilar, and supraclavicular adenopathy, accompanied by new moderate-sized pericardial and pleural effusion ( Figure 2 ).
case_images: Histopathology of metastatic hepatic lesions. (A). Intermediate power (100X) and (B). High power (1000X) view of diff quik stained smears of a fine needle aspirate of a liver nodule showing sheets and clusters of tumor cells that have scant cytoplasm and relatively uniform round nuclei with small nucleoli. (C). Intermediate (200X) and (D). high power (1000X) view of hematoxylin and eosin-stained core biopsy showing nests and cords of tumor cells with focal cribriform pattern. The tumor cells have eosinophilic cytoplasm and eccentrically placed round to oval nuclei with evenly distributed smudgy chromatin, no nucleoli, and scattered mitoses. (E). Immunostain for synaptophysin shows diffuse positivity (400X). (F). Immunostain for calcitonin shows diffuse perinuclear and cell surface staining.
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case_images: The liver lesion stained positive for calcitonin and synaptophysin, and negative for CDX2 ( Figure 3 ).
case_images: The MAPK pathway is seen on the right, and the PI-3K pathway on the left side. Genomic alterations in RET kinase including fusions and activating point mutations, lead to overactive RET signaling and uncontrolled cell growth. Selpercatinib acts to inhibit RET fusions whereas Ulixertinib is an investigational ERK1/2 inhibitor which acts downstream of MEK1 gene in MAPK pathway.
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case_images: E102-I103 that confers gain of function to (MAP2K1) MEK1 protein, acting downstream of the RET fusion ( Figure 4 ).
case_images: Brain MRI with and without contrast. The photograph illustrates an enhancing metastatic lesion located in the parasagittal left parietal lobe, measuring approximately 10 x 10 mm in diameter with mild diffusion restriction and mild surrounding vasogenic edema (white arrow).
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case_images: An MRI of the brain revealed multiple cerebral and cerebellar metastases ( Figure 5 ).