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1:
High-grade PIN
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Comments: High-grade PIN consists of intermediate to large size preexisting glands with proliferative changes resulting in hyperchromatic appearance. Note the small foci of cancer adjacent to PIN on the upper left and lower right.
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2:
High-grade PIN – Tufted Variant
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Comments: Six variants of high-grade PIN have been described – tufted, micropapillary, flat, cribriform, small cell type, and the most recent addition – inverted type. The image depicts tufted variant. Note the enlarged nuclei, prominent nucleoli and residual basal cells.
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3:
High-grade PIN – Micropapillary Variant
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Comments: The acinar epithelial cells are arranged in long, delicate, finger-like structures in this micropapillary variant. Atrophic acini are present at the bottom of the image.
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4:
High-grade PIN - Flat Pattern
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Comments: The acinar epithelial cells are pseudostratified and arranged linearly in this example of flat variant of high-grade PIN. There is nuclear and nucleolar enlargement. Note the prominent apical snouts.
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6:
High-grade PIN - Cribriform Pattern
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Comments: Distinction of cribriform variant of high-grade PIN from adenocarcinoma may at times be extremely difficult. Immunostain for high molecular weight cytokeratin 34bE12 may be useful in such cases – basal cell layer is fragmented in PIN and absent in adenocarcinoma.
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8:
High-grade PIN & Cancer - 34bE12 Immunostain
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Comments: The benign glands on upper right have continuous basal cell layer; high-grade PIN glands in the middle have fragmented basal cell layer; malignant glands on the left completely lack basal cell layer.
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9:
High-grade PIN - Prominent Nucleoli
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Comments: This example of high-grade PIN shows all the classic histologic features: intermediate-to-large size preexisting glands displaying nuclear and nucleolar enlargement and fragmented basal cell layer.
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