Ovarian small cell carcinoma in one of a pair of monozygous twins.

One of a pair of monozygous twins was diagnosed and died of small cell carcinoma of the ovary of hypercalcemic type (SCCOHT) at the age of 30 years. Her sister remained unaffected and was very concerned about her risk for developing SCCOHT. By performing comprehensive molecular analysis using whole exome sequencing (WES) approach, we showed that the deceased twin's tumour has bi-allelic somatic genetic defects (a pathogenic frameshift deletion in SMARCA4 and LOH on chr19p). Results of WES of constitutional DNA from her unaffected sister were confirmatory. Based on our findings, we concluded that the living twin is not at risk for SCCOHT and does not need to consider preventive oophorectomy.