GLP-1 receptor expression in medullary thyroid carcinoma (subject 26). A, Low-power photomicrograph (original magnification, ×100) of an H&E-stained section of medullary thyroid carcinoma (top) adjacent to nonneoplastic thyroid tissue (bottom). The tumor exhibits an organoid growth pattern and entraps thyroid follicles (asterisks). B, At higher magnification (original magnification, ×400), the tumor cells demonstrate an epithelioid to spindle cell morphology. The nuclei contain stippled chromatin giving a salt-and-pepper appearance. Nucleoli are relatively inconspicuous. C and D, Immunohistochemical staining from the same medullary thyroid carcinoma showing immunoreactivity for GLP-1R (brown; NLS1206), hematoxylin was used to counterstain the nuclei (C). As illustrated in high-power magnification, the typical staining pattern of the GLP-1 receptor (GLP-1R) is present in approximately 70% of the calcitonin-expressing medullary thyroid carcinoma C cells (D). Scale bars, 100 μm (C) and 50 μm (D). E–G, Higher-power immunofluorescent images from the same medullary thyroid carcinoma case stained for calcitonin (green, E) and GLP-1R (NLS1206; red, F). In the merged image with DAPI (blue, G), colocalization of the GLP-1R and calcitonin is indicated by the orange color. Scale bar, 50 μm.