The International System for Reporting Serous Fluid Cytopathology was recently proposed as a tiered structure to provide consistent reporting terminology for serous effusions. Because of the variation in reporting practices for indeterminate serous effusions, namely, the atypia of undetermined significance (AUS) and suspicious for malignancy (SFM) groups, the authors retrospectively reviewed cases in these 2 categories at their institution and determined the associated risk of malignancy (ROM).
Pleural, peritoneal, and pericardial effusions that were reported as AUS or SFM over a 1-year period were reviewed, and their associated ROMs were calculated based on confirmation of malignancy by previous and/or subsequent fluid and/or tissue biopsy specimens from the same general location.
In total, 145 AUS and 98 SFM serous effusion cases were identified. The AUS category was used when the cells in question lacked the requisite quantitative (cell number) and/or qualitative (morphologic) features for a definitive diagnosis. Immunohistochemistry (IHC) or flow cytometry (FCM) was available in 15% of cases (n = 22) with inconclusive results. The ROM based on 69 cases with available follow-up results was 39%. In contrast, the SFM category demonstrated cells that were morphologically suspicious for malignancy but sparse, precluding IHC or FCM (n = 63; 64%) or yielding inconclusive results (n = 35; 36%). The ROM in the SFM category, based on follow-up results of 61 cases, was 64%.
The ROM for SFM was significantly higher than that for AUS (P < .01), supporting separate diagnostic categories for these 2 groups.