Figure 2:
Biphasic Hyalinizing Psammomatous RCC case #1. The neoplasm is unencapsulated and has a rounded, nodular border with the native kidney at the top of the figure (A). The biphasic pattern is evident, as smaller cells with condensed chromatin cluster around hyalinized material while larger cells with vesicular chromatin form tubules and larger acini (B). The smaller cells also form solid spindle cell foci unassociated with basement membrane material (C). The small cells on papillae associated with basement membrane branch within larger acini, resulting in a glomeruloid pattern (D-F). The hyalinized material labels with type IV collagen, consistent with basement membrane material (G). The neoplasm has a low proliferative index as measured by Ki67 immunohistochemistry, particularly in the smaller cells (H).