Molecular profile of atypical Leydig cell tumours.

Aims: To investigate histological and copy number variations (CNVs) in Leydig cell tumours (LCTs) of the testis. Although usually benign, a small minority of cases can be associated with a poor prognosis and metastasis.

Methods: We performed whole copy number analysis to compare the genomic profile of atypical (defined by the presence of any atypical features) versus benign LCTs. Our sample consisted of one malignant (with biopsy-proven metastasis), five atypical and five benign cases.

Results: We found increased genomic instability in the malignant tumour and within two out of five (40%) atypical cases. One benign case revealed a likely pathogenic mutation in the neurofibromatosis type 2 gene, but all benign cases lacked genomic instability. Apart from the malignant case (which had metastatic spread to the scrotal skin), all remaining atypical cases did not reveal evidence of recurrence or metastatic spread.

Conclusion: CNVs by themselves are not sufficient to discriminate between cases that are benign versus those with malignant potential, without the use of histomorphological parameters. Genomic instability was only detected in the malignant and atypical cases, and not in any of the benign tumours. Thus, genomic instability may represent an early step in malignant progression. The presence of metastasis remains the only malignant criterion for LCTs.