Iso-chromosome 12p Analysis by Fluorescent In-Situ Hybridization: An Academic Institutional Experience

Introduction/Objective Chromosome 12 abnormalities like iso-chromosome 12p (i12p) and amplification of 12p are seen in majority (89%) of the primary and metastatic testicular germ cell tumors (TGCTs). i12p can be detected by karyotyping, fluorescent in-situ hybridization (FISH) or reverse transcriptase polymerase chain reaction. The aim of this study was to review i12p FISH data at our institution and assess the clinical utility. Methods/Case Report Laboratory information system was queried over a period of 15 years to search for cases where i12p FISH test was requested. FISH test was performed using TelVysion 12p telomeric probe and CEP 12 centromere probe on paraffin-embedded tissue or cell blocks. A ratio of 12ptel/CEP12 signal of 1.4 or greater was considered as positive. Patient demographics, clinical presentation, pathologic findings, and follow-up data were documented and correlated. Results (if a Case Study enter NA) Total 58 cases were identified with an age range of 14 to 76 years. Majority were male (M=52, F=6). Of these cases, 15 were testicular and 43 extra-testicular cases that included resection (n=35), biopsy (n=20) and cell-blocks (n=3). i12p was detected in 8 out of 15 testicular cases while i12p was detected in 16 out of the 43 extra-testicular cases. The extra- testicular cases included 17 retroperitoneal lesions, 8 lesions from the mediastinum, 6 lymph nodes from other sites and 12 miscellaneous lesions. Using pathology diagnosis with immunohistochemistry as gold standard, overall sensitivity was 60% and specificity was 86%. There were 3 false positive cases [Benign testicular parenchyma (n=1), suspicious for germ cell neoplasia in-situ (n=1) and undifferentiated epithelioid neoplasm (n=1)]. Conclusion Our results show that although the sensitivity was limited, FISH test for i12p demonstrated high specificity(86%) for diagnosis of primary or metastatic TGCTs. As an adjunct test, i12p FISH can help identify and further characterize a significant number of GCTs with unusual morphology or clinical presentation.