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Serous Borderline Tumor with Micropapillary Features (MSBT): Figures 7-11. Serous borderline tumors containing micropapillary growth in an area measuring greater than 5mm are classified as MSBT. Note the contrast between serous borderline tumor at the top of Figure 7 and extensive micropapillary growth at the bottom. More proliferative examples, Figures 8-9, show long, slender micropapillae surrounding large fibrovascular cores without hierarchical branching. Figure 10 shows both micropapillary and cribriform growth patterns. The cytologic grade of MSBTs should not exceed grade 2 of 3; Figure 11 illustrates a MSBT with cytologic atypia at the high end of the spectrum permitted for this diagnosis. Submitted by Robert A. Soslow, MD