Bilateral germ cell tumor of the testis (TGCT): Implications for a stem cell versus genetic origin of cancers.

428 Background: Bilateral TGCT offers a unique opportunity to elucidate a stem cell versus genetic origin of cancer (Coffey, 2008). Comparison of the epigenetics and genetics of disparate tumors in either synchronous or metachronous bilateral TGCT from the same patients is feasible and may be informative. Methods: We examined the clinical characteristics and natural history of 37 patients with bilateral TGCT. We performed reduced representation bisulfite sequencing (RRBS) of FFPE DNA and whole exon sequencing (WES) of 5 of those patients whose tumor samples were available for the study. Results: We identified 37 patients with bilateral TGCT, who underwent their first orchiectomy between January 1984 and April 2022 and the second between August 1997 and April 2022. Thirty-five (95%) of these patients are still alive. Seven patients had synchronous, while 30 had metachronous bilateral TGCT. There were 13 bilateral seminomas, 14 bilateral nonseminomas, and 10 bilateral seminoma and nonseminoma. For those patients with metachronous bilateral TGCT, the median time between the two TGCT was 59 months (range 6-400). WES revealed a mutation in 189 (<1%) out of about 20,000 genes in the 10 paired samples from 5 patients. A total of 2 genes were mutated in more than 1 sample: KIT (n=4), and KRAS (n=2). Although one patient with synchronous bilateral seminomas shared KIT mutation, another did not with KIT and KRAS mutations (Table). RRBS showed a similar methylation profile in the 2 metachronous nonseminomas, which did not share any genetic mutations in the WES study. Conclusions: The clinical course of our patients with synchronous and metachronous bilateral TGCT and the results of our RRBS and WES reaffirmed that a preponderance of TGCT was curable and alluded to whether its epigenetic vs genetic origins might be causative or contributory to its general curability vs potential lethality. Coffey J et al. Somatic KIT mutations occur predominantly in seminoma germ cell tumors and are not predictive of bilateral disease: report of 220 tumors and review of literature. Genes Chromosomes Cancer 2008;47:34-42. [Table: see text]