Isochromosome 12p and polysomy 12 in primary central nervous system germ cell tumors: frequency and association with clinicopathologic features

Germ cell tumors arising within the central nervous system are rare neoplasms that typically occur along midline structures in children and young adults. Although isochromosome 12p is established as a frequent chromosomal abnormality in testicular germ cell tumors, studies examining isochromosome 12p in primary central nervous system germ cell tumors are limited. Herein, we studied 24 primary central nervous system germ cell tumors from 23 patients using fluorescence in situ hybridization to determine the frequency of isochromosome 12p in these neoplasms. Of the 24 primary central nervous system germ cell tumors, fluorescence in situ hybridization detected isochromosome 12p in 6 (25%) tumors, whereas 11 (46%) tumors showed polysomy (multiple copies) of chromosome 12. One case with isochromosome 12p also showed increased 12p independent of isochromosome 12p formation. The remaining 7 tumors yielded a normal result by fluorescence in situ hybridization. Clinical follow-up of this patient cohort indicated 8 patients (32%) developed a recurrence, although no association was demonstrated between the presence or absence of chromosomal 12 abnormalities and tumor relapse. We confirm that isochromosome 12p is less frequent in primary central nervous system germ cell tumors relative to testicular germ cell tumors, and although our numbers are limited, the presence or absence of isochromosome 12p does not appear to impact tumor recurrence. Similarly, although polysomy 12 was identified in nearly half of our central nervous system germ cell tumors, no prognostic significance was attributed to this abnormality. These results suggest that fluorescence in situ hybridization studies for isochromosome 12p or polysomy 12 may have limited use in the evaluation of these rare neoplasms.