Fig 1.

Samples from individual with germline BRCA2 5193delC mutation demonstrating a secondary somatic mutation restoring BRCA2 in her ovarian carcinoma. (A) Lymphocyte DNA sequence of the heterozygous germline BRCA2 5193delC mutation. (B) DNA sequence from her primary ovarian carcinoma. Only mutant 5193delC sequence is seen, consistent with loss of the wild-type BRCA2 allele in neoplastic cells. (C) DNA sequence from recurrent ovarian carcinoma obtained 10 years after initial diagnosis. This patient had multiple chemotherapeutic regimens for recurrent disease, including a poly (ADP-ribose) polymerase (PARP) inhibitor before surgical resection of this recurrence (CS1 in Table 1). An insertion of an A base is seen at nucleotide 5177, which restores the open reading frame disrupted by the 5193delC mutation and restoring full-length BRCA2 protein. Both the original BRCA2 5193delC sequence and the 5177insA/5193delC combination sequence are seen, suggesting that the secondary mutation occurs in just one of a duplicated mutant allele or in just a proportion of the neoplastic cells analyzed. Postoperatively, the recurrent carcinoma was resistant to platinum chemotherapy and subsequently to a trial of a PARP inhibitor. (D) Single nucleotide polymorphism (SNP) haplotyping differentiates the germline mutant and wild-type alleles. Lymphocyte DNA demonstrates an A/G SNP within BRCA2. The primary carcinoma has only G, indicating that the G is on the mutant allele. The recurrent carcinoma also has predominantly G, indicating that the secondary mutation occurred on the mutant allele. (E) Allele diagrams show the relative positions of the SNP, the original mutation, and the secondary mutation.