Triple-color FISH analysis of 12p amplification in testicular germ-cell tumors using 12p band-specific painting probes

Forty-nine surgical specimens and nine germ cell tumor lines were analyzed by triple-color FISH using microdissected probes for the cytogenetic bands of chromosome arm 12p (12p11.2, p12, and p13). FISH analysis demonstrated amplification of material from all three bands in all tumors. This amplification was in the form of increased copy number of 12p or i(12p) and/or 12p amplified regions (AMP12p). The number of copies of 12p was variable (4-11 copies) from case to case but tended to remain relatively constant in all clones of the same tumor, even when the amplification took the form of an amplified region composed of 12p material. In tumors with multiple clones, i(12p) and AMP12p were never found in the same cell. No correlation was found between 12p copy number and tumor type. We describe, for the first time, a relative overrepresentation of 12p13 or 12p12-p13 regions in six tumors (two surgical samples and four cell lines), either as "partial 12p" (five cases) or within a 12p amplified region (one case). The ubiquitous amplification of all three 12p bands in germ-cell tumors supports the hypothesis that 12p harbors more than one gene important for oncogenesis of adult male germ-cell tumors, and that these genes may be located in different areas of 12p.