Background A giant congenital melanocytic nevus (GCMN) is found in 0.1% of live-born infants. If present, the lesion has a chance of about 6% to develop into malignant melanoma. Both children and adults can be affected by malignant melanoma arising in a giant congenital nevus. Up to 95% of GCMNs harbor NRAS mutations, and mutations in the BRAF , MC1R , TP53 , and GNAQ genes have also been described. The individualization of therapy is required, but diagnostic and prognostic criteria remain controversial. Case presentations We report two cases: 1) melanoma arising in a giant congenital nevus during the first month of life complicated with neurocutaneous melanosis (NCM), and 2) melanoma arising in a giant congenital nevus during the first 6 months of life. Pathology, immunohistochemistry, and genetic analyses of tumor tissue were performed. The first case revealed only a non-pathogenic P72R polymorphism of the TP53 gene in the homozygote condition. For the second case, a Q61K mutation was detected in the NRAS gene. Conclusion Malignant melanoma associated with GCMN is rare and therefore poorly understood. Outcomes have been linked to the stage at diagnosis, but no additional pathological prognostic factors have been identified. The most frequent genetic event in giant CMNs is NRAS mutations, which was discovered in one of our cases. To accumulate evidence to improve disease prognosis and outcomes, children with congenital melanocytic nevus should be included in a systemic follow-up study from birth.

Medullary thyroid carcinoma (MTC) occurs as a sporadic tumor or in connection with inherited cancer syndromes of multiple endocrine neoplasia type 2 and familial MTC. Missense RET proto-oncogene mutations and small in-frame deletions are found in most of the cases. In a significant amount of sporadic MTC cases somatic mutation at codon 918 (exon 16), or at codons 609, 611, 618, 620 (exon 10), or codons 630, 634 (exon 11) appear. We report here on three new somatic cell missense mutations of the RET proto-oncogene associated with sporadic MTC. In one tumor mutation at codon 922 TCC(Ser)-->TTC(Phe) in exon 16 was found. In another tumor two mutations at codons 639 GCA(Ala)-->GGA(Gly) and 641 GCT(Ala)-->CGT(Arg) in the exon 11 were observed. Allele-specific PCR followed by sequencing demonstrated the presence of both mutations at the same allele.

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