Molecular Genetic Evidence of an Independent Origin of Serous Low Malignant Potential Implants and Lymph Node Inclusions

Patients with ovarian serous tumors of low malignant potential (LMP) are commonly found to have peritoneal implants. Less commonly, similar lesions are seen in lymph nodes, sometimes in association with endosalpingiosis. We compared these lesions to the coexisting ovarian LMP tumors to determine whether they are clonally related to the ovarian neoplasm. Seventeen patients with serous LMP tumors present at 2 or more sites were identified. Tissue samples were microdissected from formalin-fixed paraffin-embedded tissue blocks. Samples of normal tissue, the ovarian LMP tumors, peritoneal LMP implants, and LMP inclusions within lymph nodes were obtained. Genomic DNA was extracted from the samples, and polymerase chain reaction and X-chromosome inactivation (human androgen receptor assay) analysis were performed. The pattern of X-chromosome inactivation could be determined in 15 of the 17 cases, and nonrandom X-chromosome inactivation was observed in 13 of these cases. Twelve of these cases included both ovarian and extraovarian LMP tumors. In 9 of these 12 cases, the extraovarian LMP tumor shared a similar pattern of nonrandom X-chromosome inactivation with the ovarian tumor. In these cases, the shared inactivation pattern was seen at 1 extraovarian site (3 cases), 2 extraovarian sites (4 cases), 5 extraovarian sites (1 case), and 7 of 8 extraovarian sites (1 case). In the remaining 3 cases, opposite patterns of nonrandom X-chromosome inactivation were seen. These data suggest that, in most cases, serous LMP tumor implants and lymph node inclusions share a common clonal origin with the associated ovarian tumors. However, in at least some cases, the implants and inclusions seem to arise independently from the associated ovarian serous LMP tumors.