No familial marker chromosome associated with a malignancy has been re
ported to date. We used fluorescence in situ hybridization (FISH) to c
haracterize a supernumerary marker chromosome 15 ascertained during pr
enatal diagnosis. This supernumerary chromosome 15 was found to span t
hree generations of a family. Three family members carrying the supern
umerary chromosome 15 have also had malignancies, namely, a cystic gli
oma, leukemia, and thyroid cancer.