Cytogenetic Markers

Some progress has been made in the search for genetic markers in GCTs. In 1983, Atkin and Baker located the first specific chromosomal abnormality associated with GCTs.37 They noted duplication of the short arm of chromosome 12, designated i(12p), in four patients with testicular neoplasms. Larger series later confirmed extra copies of i(12p) in 83% of male GCTs; moreover, its presence was noted in all histologic types, including 89% of SGCTs and 81% of NSGCTs, and in all pathologic stages.38 The occurrence of this cytogenic marker in other tumors is unusual, making it an ideal candidate for a useful histologic tumor marker.13 Indeed, in one study, i(12p) was used to make the definitive diagnosis in 28% of patients with poorly differentiated carcinomas of unknown origin.39 Also, there is some evidence that the presence of more than three copies of i(12p) predicts a poor response to chemotherapy.40 On a more experimental front, a recent study by Summersgill and colleagues found a gain of i(12p) material in invasive tumors but not in testicular carcinoma in situ (CIS)41; this suggested a role in progression to invasion. Others, however, have found rare cases of CIS exhibiting i(12p); this has been interpreted as evidence of a key and early role for i(12p) in tumorigen-esis.42 One possible explanation for this defect is that its mechanism of action is exerted through the proto-oncogenes cyclin D and parathyroid hormone-like hormone (PTHLH), both of which are localized on

12p. These oncogenes, however, have yet to be shown to have a significant impact in GCTs. Obviously, the exact clinical value of i(12p) is still evolving.

Parenthetically, other chromosome alterations, involving loci on chromosomes 1 to 13, 17, 18, 22, and X, have been implicated in GCT pathogenesis and prognosis.38-48 This important work, however, is still in its infancy, and detailed discussion of each of these loci is beyond the scope of this chapter.

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