Morphological Characteristics of Pleural Mesothelioma Cells Harboring 9p21 Homozygous Deletion Detected by Fluorescence In Situ Hybridization (FISH) in Effusion Cytology
Makoto Hamasaki, Shinji Matsumoto, Kazuki Nabeshima, Toshiaki Kamei, Kenzo Hiroshima, Yoshihiro Matsuno, Kunimitsu Kawahara, Tohru Tsujimura. Fukuoka University Hospital, Fukuoka, Japan; Yamaguchi Grand Medical Center, Hofu, Japan; Tokyo Women's Medical University Yachiyo Medical Center, Yachiyo, Japan; Hokkaido University Hospital, Sapporo, Japan; Osaka Prefectural Medical Center for Respiratory and Allergic Disease, Habikino, Japan; Hyogo College of Medicine, Hyogo, Japan
Background: In malignant pleural mesothelioma (MPM), cytologic analysis is the primary diagnostic approach, since most patients first present with pleural effusion. However, the cytologic distinction between MPM and reactive mesothelial cells (RMC) in effusions can be impossible sometimes due to the lack of both well-established immunocytochemical markers and definite cytological criteria for MPM. Homozygous deletion of the 9p21 locus, the site of the CDKN2A/p16 gene, frequently occurs in MPM but so far has never been reported in RMC. The aim of this study was to define the cytomorphological characteristics of MPM cells, identified by the presence of 9p21 homozygous deletion by FISH.
Design: For the above purpose, cells on smear preparations were recorded using a virtual microscope system, and then subjected to FISH analysis. Thereafter, 9p21 homozygous deletion-positive cells (about 100 cells each case) were identified in the recorded virtual slides, followed by analysis of their morphological characteristics. The study material comprised 61 histopathological (45 MPM + 16 RMC) and 13 cytological (7 MPM + 6 RMC) cases.
Results: Cut-off values (>10% for homozygous deletion and >52% for heterozygous deletion) were set based on the results of 9p21 FISH in tissue sections. According to the cut-off values, all effusion cases of MPM were 9p21 homozygous deletion-positive, whereas none of RMC cases was deletion-positive.
Conclusions: The 9p21 homozygous deletion-positive MPM cells exhibited significantly more frequent cell-in-cell engulfment, multinucleation, especially more than three nuclei, and larger multicellular clusters composed of more than 10 cells, compared with 9p21 deletion-negative RMC, indicating that these findings are useful for cytological differentiation of MPM cells from RMC.Our study also introduced a new methodology to analyze the morphology of a tumor using the combination of the virtual microscope system and FISH.
Wednesday, March 21, 2012 9:30 AM
Poster Session V # 294, Wednesday Morning