The implications of BRCA loss of heterozygosity (LOH) and deficient mismatch repair gene (dMMR) expression in the breast cancer of a patient with both inherited breast and ovarian cancer syndrome (BRCA2) and Lynch syndrome (MLH1)

Breast Cancer Res Treat. 2020 Apr;180(2):511-514. doi: 10.1007/s10549-020-05569-7. Epub 2020 Feb 10.

Abstract

Background: BRCA germline pathogenic variants represent the most common inherited mechanism predisposing individuals to breast cancer, while germline pathogenic variants in one of the mismatch repair (MMR) genes represent the most common colon cancer-predisposing inherited syndrome, known as the Lynch syndrome (LS). Individuals who harbor pathogenic germline variants for both syndromes are extremely rare. Germline testing is now done routinely for patients with breast cancer and MMR testing is recommended for nearly all patients diagnosed with colon or rectal cancer (Benson et al in NCCN clinical practice guidelines in oncology (NCCN guidelines) colon cancer (Version 4.2019-November 8, 2019). www.NCCN.org, Gradishar et al in NCCN clinical practice guidelines in oncology (NCCN guidelines) breast cancer (Version 3.2019-September 6, 2019).www.NCCN.org). We report a patient with germline mutations in both BRCA2 and the MMR gene MLH1 who developed breast cancer. The breast cancer showed loss of heterozygosity (LOH) in BRCA2 (the molecular hallmark of cancers related to inheritance of a BRCA alteration) and was also deficient in mismatch repair gene protein expression (dMMR), the hallmark of LS-related cancers. We discuss the possible mechanisms of transformation that would explain the finding that the tumor showed both BRCA2 LOH and was dMMR, each of which would generally be considered a gatekeeper event for transformation of normal cells to malignancy.

Results: This report describes a patient with molecularly diagnosed breast and ovarian cancer syndrome (BRCA2) and LS. Next generation sequencing (NGS) and immunohistochemical (IHC) testing demonstrated her breast cancer to show BRCA2 LOH and to be dMMR.

Conclusion: The patient presented represents the first reported case where both next generation sequencing (NGS) for BRCA LOH and MMR IHC testing of her breast cancer were performed and underscores the importance of using NGS including the reported mutational allelic frequency (MAF) and IHC use to predict the likely responsiveness to the recently approved PARP inhibitors and checkpoint inhibitor therapies (Robson et al in N Engl J Med 377:523-533, 2017, Lemery et al in 377(15):1409-1412, https://doi.org/10.1056/NEJMp1709968, 2017), key because the gatekeeper transforming event for tumors related to inherited cancer syndromes is loss of normal tumor suppressor gene (TSG) protein expression.

Keywords: BRCA; Lynch syndrome; Mutational allelic burden.

Publication types

  • Case Reports

MeSH terms

  • BRCA2 Protein / genetics*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology*
  • Colorectal Neoplasms, Hereditary Nonpolyposis / genetics
  • Colorectal Neoplasms, Hereditary Nonpolyposis / pathology*
  • Female
  • Genetic Predisposition to Disease
  • Germ-Line Mutation*
  • Humans
  • Immunotherapy / methods
  • Loss of Heterozygosity*
  • Middle Aged
  • Molecular Targeted Therapy / methods
  • MutL Protein Homolog 1 / genetics*
  • Ovarian Neoplasms / genetics
  • Ovarian Neoplasms / pathology*
  • Prognosis

Substances

  • BRCA2 Protein
  • BRCA2 protein, human
  • MLH1 protein, human
  • MutL Protein Homolog 1

Supplementary concepts

  • Breast Cancer, Familial