RESUMEN
BACKGROUND: Cases of children with more than one type of cancer either diagnosed simultaneously or successively, rarely occur in pediatric oncology. A second malignant neoplasm may be caused by mutagenic effects of the treatment of the primary malignancy and/or may point towards an underlying genetic cancer susceptibility syndrome. One example of such a syndrome is constitutional mismatch repair-deficiency, (CMMR-D) which carries an increased risk of various tumors including childhood hematologic malignancies and Lynch syndrome associated tumors. Timely diagnosis of CMMR-D is crucial, since this diagnosis has implications for the entire family. PATIENT: We report the case of a 15-year-old girl who was born to consanguineous parents. At the age of 20 months she was diagnosed with a T-cell non-Hodgkin lymphoma. Treatment was given according to NHL-BFM 95. 12 years later, an invasive adenocarcinoma of the colon was surgically removed which relapsed shortly afterwards. METHODS: Whole-exome sequencing of germline DNA was employed to rapidly detect the underlying mutation in this suspected CMMR-D patient. RESULTS: After a short turnaround time of less than 3 weeks, the diagnosis of CMMR-D could be confirmed by the identification of a homozygous 29-bp deletion in MSH6 (exon 6), which was confirmed by independent methods. CONCLUSIONS: We demonstrate that "bed-side" whole-exome sequencing is both feasible and cost-effective and may be the method of choice to rapidly uncover the genetical basis of (inherited) diseases.