Isochromosome of the short arm of chromosome 12: clinically useful markers for male germ cell tumors.

Twenty-nine tumor specimens were obtained from 24 males with germ cell tumors. All primary sites and histologies were represented. An isochromosome of the short arm of chromosome 12 [i (12p)] was found in 20 specimens obtained from 16 patients, a 46,XY normal karyotype was present in seven specimens, and one specimen was a cytogenetic failure. The i(12p) was found in tumors from all primary sites and in all histologies, including a choriocarcinoma. The presence of three or more additional copies of 12p was associated with a statistically significant greater likelihood of treatment failure. With diagnostic and possibly prognostic importance in germ cell tumors in males, the high frequency of i(12p) in our series of studies and in those of others indicates that it probably occurs as a very early defect in the development of these tumors. Further studies of chromosome 12 in males with these tumors are warranted.