Establishing germ cell origin of undifferentiated tumors by identifying gain of 12p material using comparative genomic hybridization analysis of paraffin-embedded samples.

An estimated 10% of adult cancer patients present with undifferentiated carcinoma. The diagnosis of germ cell tumor (GCT) in such patients can be difficult but has important implications for patient management. Male testicular GCT is characterized by an isochromosome 12p, i(12p), or additional 12p material, in some cases restricted to the 12p11.2-p12.1 region. A gain of 12p material can indicate that a tumor, which may not be present in the testis, is of germ cell origin. Formalin-fixed, paraffin-embedded samples are the most widely available material for diagnostic analysis and retrospective studies. We have compared the identification of 12p gain in snap-frozen samples with corresponding paraffin-embedded material from three clearly defined testicular GCTs using comparative genomic hybridization analysis. In this preliminary study, paraffin-embedded tumor samples of uncertain histogenesis from seven patients were then analyzed. Tumor samples from three of these patients showed a gain of 12p material, and in one patient, gain was restricted to the 12p11.2-p12 region. The clinical picture and response to therapy were generally consistent with the 12p status, though lack of 12p gain may not exclude a diagnosis of GCT.