2018 Volume 57 Issue 2 Pages 101-108
Many pathologists as well as cytotechnologists experience difficulty when making a cytological diagnosis of malignant mesothelioma (MM). To address this, a working group on MM cytology examination of the Japan Lung Cancer Society was started and practical cytological diagnostic criteria for MM were created. In the criteria, significant cytomorphological findings for the accurate diagnosis of MM using pleural effusion are as follows : 1) characteristic background composed of hyaluronic material ; 2) presence of type Ⅱ collagenous stroma ; 3) occasional presence of cell-in-cell engulfment with a cytoplasmic projection called a “hump” ; 4) deeply stained thick cytoplasm ; 5) ambiguous cell surface ; 6) frequent Orange G-positive cells ; 7) high frequency of multinucleated cells. As for immunocytochemistry, two mesothelial markers (among calretinin, WT1, and D2-40), and two carcinoma markers (among CEA, MOC-31, Ber-EP4, TTF-1 and napsin A) are recommended for differentiating MM from reactive mesothelial cells (RM). EMA (membranous pattern), desmin, Glucose transporter 1 and CD146 are recommended for differentiating MM from RM. Moreover, the homozygous deletion of p16 (CDKN2A) detected by FISH (Fluorescence in situ hybridization) and the loss of BRCA-associated protein 1 (BAP1) by immunocytochemistry are very useful for differentiating MM from RM. These criteria provide a practical reference for pathologists as well as cytotechnologists.
