Detection of numerical aberrations of chromosomes 7 and 9 in cytologic specimens of pleural malignant mesothelioma

BACKGROUND. Accurate diagnosis of malignant mesothelioma (MM) in effusion fluid specimens can be challenging. Previous cytogenetic studies demonstrated that chromosomal aneusomy is commonly associated with MM. The authors attempted to determine whether the detection of numerical chromosomal aberrations in the effusion fluid specimens could be a useful diagnostic adjunct in morphologically inconclusive cases for MM. METHODS. The authors analyzed 17 cytologic specimens (15 pleural fluids, 2 fine-needle aspirates) of histologically confirmed MM obtained from 16 patients using fluorescent in situ hybridization (FISH) with centromeric chromosome 7 and 9 probes. Seventeen benign pleural effusion fluid specimens containing reactive/ benign mesothelial (RM) cells were used as controls. After destaining of Diff-Quik-stained smears, the slides were hybridized using a standard FISH protocol. One hundred cells/probe/case were counted manually. RESULTS. For chromosome 7, polysomy (defined as greater than or equal to 3 signals/nucleus in >10% of the cells) was present in 88% and 0% of the MM and the RM cases, respectively. Trisomy (defined as 3 signals/nucleus in > 5% of the cells) was present in 77% and 0% of the MM and the RM cases, respectively. Tetrasomy (defined as 4 signals/ nucleus in > 10% of the cells) was present in 29% and 0% of the MM and the RM cases, respectively. The mean values of positive cells showing polysomy 7 and trisomy 7 were markedly different in MM and RM cases (39% vs. 4% and 31% vs. 1%, respectively). The frequency of polysomy 9 and trisomy 9 in MM and RM cases was 69% vs. 13% and 62% vs. 6%, respectively. CONCLUSIONS. These results suggest that polysomy of chromosome 7 or 9 is a common finding in MM but uncommon in RM. Therefore, in conjunction with cytomorphologic and clinical suspicion of MM, detection of numerical chromosomal aberrations of chromosome 7 using FISH with routine cytologic smears can be a valuable diagnostic adjunct.