Molecular and cytogenetic studies in the diagnosis of patients with poorly differentiated carcinomas of unknown...

A minority of patients with poorly differentiated carcinoma achieve a complete response to cisplatin therapy. Recently, specific chromosomal abnormalities have been described for several solid tumor malignancies. Molecular and cytogenetic techniques were used to study tumors of patients with midline carcinoma of unknown primary site.

Forty patients with poorly differentiated carcinoma of unknown primary site had fresh tumor samples studied by cytogenetic analysis, Southern blot analysis for 12p copy number, and fluorescence in situ hybridization (FISH) for the identification of i(12p) and chromosome 12 aneuploidy. The response to cisplatin therapy was correlated to the diagnosis provided by the genetic studies.

In 17 (42%) patients, a diagnosis was suggested by the genetic studies. This included a germ cell tumor in 12 (30%) patients by the finding of i(12p), increased 12p copy number, or a deletion of the long arm of chromosome 12. In five patients, a specific diagnosis other than germ cell tumor was suggested by tumor karyotype. These were neuroepithelioma, lymphoma, desmoplastic small-cell tumor, melanoma, and clear-cell sarcoma. The 75% response proportion to cisplatin therapy in patients with tumors showing chromosome structural abnormalities of germ cell tumor was greater than the 18% response proportion in patients for whom no diagnosis was provided (P = .002).

Molecular and cytogenetic studies are useful in establishing specific diagnoses in patients with poorly differentiated carcinomas of unknown primary site. This group of tumors is heterogeneous and is composed of germ cell tumors, melanoma, lymphoma, neuroepithelioma, and desmoplastic small-round-cell tumor in addition to some that are not yet classifiable. Response to cisplatin therapy correlates with the finding of i(12p) in tumor by either molecular or cytogenetic studies.