PMC8387080_01
Papillary thyroid carcinoma with nodular fasciitis-like stroma. A - A non-encapsulated and well circumscribed tumor showing a biphasic growth pattern with surrounding normal thyroid parenchyma (H&E, 4x); B - The epithelial component showing an arrangement in the form of tubulo-papillary and leaf-like or animal-like patterns (H&E, 10x); C - The tumor cells are in a single layer with characteristic nuclear chromatin clearing, grooving, and pseudo-inclusions at places (H&E, 40x); D - The stroma element shows fascicular arrangement with uniform proliferating benign spindle cells indicating a reactive nature (H&E, 10x).
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The predominant component was formed by a stromal element (65%-70%) with intervening epithelial component (30%-35%) (Figure 1A). The epithelial component showed tubular and papillary configuration, and at various places, it was compressed by the stromal component in a leaf-like or animal-like configuration (Figure 1B). Some tumor cells displayed optically clear chromatin, nuclear grooving, and nuclear pseudoinclusion (Figure 1C). The mesenchymal element appeared mild to moderately cellular, and contained uniform, spindle-shaped stromal cells in fascicular arrangement (Figure 1D).
A - The epithelial component shows diffuse strong cytoplasmic granular positivity for the BRAF mutant protein (10x); B - diffuse weak membranous positivity for beta-catenin (20x); C - and variable nuclear positivity for PAX8 (20x). The stromal component was negative for BRAF, beta-catenin and PAX8 immunostains. D - Lymph node metastasis showing only the epithelial component (H&E, 20x).
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TTF-1, thyroglobulin, BRAF V600E mutant protein (VE1 clone, Ventana) (Figure 2A), beta-catenin (membranous positivity; Figure 2B), PAX8 (Figure 2C), pan cytokeratin, CK7, and BCL2 (weak). The stromal cells showed positivity for smooth muscle actin (focal) and vimentin, whereas it was negative for beta-catenin and BCL2. However, in the metastatic site, only the epithelial component was detected, showing features of classical papillary carcinoma without the presence of a stromal component (Figure 2D).