Teratomatous genotype detected in malignancies of a non-germ cell phenotype

Originating from post-meiotic germ cells, mature ovarian teratomas (MOT) are genetically homozygous tumors within heterozygous hosts. MOT may be associated with malignant tumors of a non-germ cell phenotype (so-called malignant transformation). Based on the presence of in situ changes, some cases have been hypothesized to arise from teratomatous tissue. However, other malignancies associated with mature teratomas, such as sarcomas, may originate from either teratomatous elements or preexisting somatic ovarian tissue. Eight cases of MOT containing various histologic types of malignancy, including four squamous cell carcinomas, two sarcomas, one thyroid carcinoma, and one carcinoid tumor, were selected for study. Using selective tissue microdissection and PCR-based analysis of the extracted DNA, we compared the genotypic pattern of the mature teratomatous components to the associated malignant neoplasm with a random panel of highly informative genetic markers for different chromosomes. In all eight cases, genetic analysis of the malignant component revealed a homozygous genotype. In seven cases, the genetic profiles of mature teratomas and the associated malignant tumors were identical, suggesting a direct pathogenetic relationship between these lesions. In one case, the malignant component revealed homozygosity of different alleles compared with mature teratoma, suggesting independent teratomatous growth processes. This finding indicates that some ovarian malignancies of the non-germ cell phenotype arise in teratoma and fall into the spectrum of germ cell tumors.