Absence of isochromosome 12p in a pineal region malignant germ cell tumor.

We report the first cytogenetic investigation of a rare pineal region mixed germ cell tumor. The mean modal number was 78. Multiple numerical and structural abnormalities were noted. Chromosomes 21 and 1q were consistently overrepresented, and chromosome 13 was underrepresented. A translocation involving chromosome 11 occurred in all metaphases examined. The Y chromosome was lost, and three copies of the X chromosome were present. No isochromosome 12p was identified, but four copies of chromosome 12 were present.