[1888] Diagnostic Utility of p16 FISH in Distinguishing between Biphasic Mesothelioma and Epithelioid Mesothelioma

Kenzo Hiroshima, Di Wu, Kazuki Nabeshima, Toshikazu Yusa, Daisuke Ozaki, Yukio Nakatani, Toshiro Nishikawa. Tokyo Women's Medical University Yachiyo Medical Center, Yachiyo, Chiba, Japan; Fukuoka University, Fukuoka, Japan; Chiba Rosai Hospital, Ichihara, Chiba, Japan; Chiba University, Chiba, Japan; Tokyo Women's Medical University, Tokyo, Japan

Background: Some of biphasic mesotheliomas may be difficult to distinguish from epithelioid mesothelioma with atypical fibrous stroma. Prognosis of patients with biphasic mesothelioma is reported to be worse than that of epithelioid mesothelioma, but better than that of sarcomatoid mesothelioma. The aim of this study was to analyze the p16 deletion in epitheliod and sarcomatoid component of biphasic mesothelioma and define the diagnostic criteria of biphasic mesothelioma.
Design: We analyzed 48 cases of pleural mesothelioma. Tumors were grouped into three categories: epithelioid, sarcomatoid and biphasic mesothelioma. Fluorescence in situ hybridization (FISH) of p16 was performed on formalin-fixed, paraffin-embedded sections using dual color locus-specific p16 probe. Both epithelioid and sarcomatoid component was analyzed separately in eight cases of biphasic mesothelioma and two cases of sarcomatoid mesothelioma with minor component of epitheliod subtype. FISH analysis was also performed in three cases of epithelioid mesothelioma with atypical cellular fibrous stroma.
Results: The percentages of homozygous deletion are 55.6% (10/18), 100% (22/22), and 87.5% (7/8) in epithelioid, sarcomatoid, and biphasic mesothelioma, respectively. Both epitheliod and sarcomatoid component harbor homozygous deletion of p16 in seven of biphasic mesotheliomas and two of sarcomatoid mesotheliomas with minor component of epithelioid subtype. In one of biphasic mesotheliomas, both component lacks homozygous deletion of p16. Fibrous stroma in three epitheliod mesotheliomas does not harbor homozygous deletion of p16. The median survival for patients are 22 months for epithelioid mesothelioma, 12 months for biphasic mesothelioma, and 5 months for sarcomatoid mesothelioma (p = 0.0015). p16 homozygous deletion is associated with shorter survival.
Conclusions: p16 is deleted in all of sarcomatoid mesotheliomas. Frequency of p16 deletion in biphasic mesothelioma is higher than that in epithelioid mesothelioma contrary to the description in 2012 IMIG guidelines for pathological diagnosis of mesothelioma. Deletion of p16 should be confirmed in fibrous component of mesothelioma when the distinction between biphasic mesothelioma and epithelioid mesothelioma with atypical fibrous stroma is difficult.
Category: Pulmonary

Wednesday, March 6, 2013 1:00 PM

Poster Session VI # 282, Wednesday Afternoon


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