The presence of SFTs of the pleura in a mother and daughter may be due to chance, exposure to a common environmental agent, or due to a germ-line mutation that was genetically transmitted. An SFT of the pleura is an uncommon neoplasm. Only about 800 cases have been reported.7The gene or chromosome responsible for SFTs of the pleura has not yet been identified. Different cytogenetic studies of SFTs of the pleura have reported8–11 varying mutations in chromosome number (eg, trisomy 8, trisomy 21, and trisomy 5). Miettinen and coworkers,,10 using comparative genomic hybridization, showed that changes in DNA copy number occurred more commonly in those SFTs that were > 10 cm and in those with greater mitotic activity. Various more complex translocations have been found as well. A break point in chromosome 4 was found in case reports of SFTs in both pleural and peritoneal locations,12–13 but this has not been confirmed in other studies. Given that no consistent chromosomal abnormality has been reported, further cytogenetic or molecular genetic investigations of SFTs of the pleura are needed before their genetic etiology can be known.