Li-Fraumeni syndrome: not a straightforward diagnosis anymore-the interpretation of pathogenic variants of low allele frequency and the differences between germline PVs, mosaicism, and clonal hematopoiesis.

The introduction of next-generation sequencing has resulted in testing multiple genes simultaneously to identify inherited pathogenic variants (PVs) in cancer susceptibility genes. PVs with low minor allele frequencies (MAFs) (< 25-35%) are highlighted on germline genetic test reports. In this review, we focus on the challenges of interpreting PVs with low MAF in breast cancer patients undergoing germline testing and the implications for management.The clinical implications of a germline PV are substantial. For PV carriers in high-penetrance genes like BRCA1, BRCA2, and TP53, prophylactic mastectomy is often recommended and radiation therapy avoided when possible for those with Li-Fraumeni syndrome (LFS). For germline PV carriers in more moderate-risk genes such as PALB2, ATM, and CHEK2, annual breast MRI is recommended and prophylactic mastectomies considered for those with significant family histories. Detection of PVs in cancer susceptibility genes can also lead to recommendations for other prophylactic surgeries (e.g., salpingo-oophorectomy) and increased surveillance for other cancers. Therefore, recognizing when a PV is somatic rather than germline and distinguishing somatic mosaicism from clonal hematopoiesis (CH) is essential. Mutational events that occur at a post-zygotic stage are somatic and will only be present in tissues derived from the mutated cell, characterizing classic mosaicism. Clonal hematopoiesis is a form of mosaicism restricted to the hematopoietic compartment.Among the genes in multi-gene panels used for germline testing of breast cancer patients, the detection of a PV with low MAF occurs most often in TP53, though has been reported in other breast cancer susceptibility genes. Distinguishing a germline TP53 PV (LFS) from a somatic PV (TP53 mosaicism or CH) has enormous implications for breast cancer patients and their relatives.We review how to evaluate a PV with low MAF. The identification of the PV in another tissue confirms mosaicism. Older age, exposure to chemotherapy, radiation, and tobacco are known risk factors for CH, as is the absence of a LFS-related cancer in the setting of a TP53 PV with low MAF. The ability to recognize and understand the implications of somatic PVs, including somatic mosaicism and CH, enables optimal personalized care of breast cancer patients.

Family communication and patient distress after germline genetic testing in individuals with pancreatic ductal adenocarcinoma.

BACKGROUND: Germline genetic testing currently is recommended for patients with pancreatic ductal adenocarcinoma (PDAC). In the current study, the authors assessed how often results are communicated to first-degree relatives within 3 months and the emotional impact of testing on patients. METHODS: A total of 148 patients who were newly diagnosed with PDAC and who had undergone testing of 32 cancer susceptibility genes at 3 academic centers were selected; 71% participated. Subjects completed the Multidimensional Impact of Cancer Risk Assessment (MICRA) and a family communication survey. The results of both surveys were assessed at 3 months according to the genetic test result (positive, negative, or variant of unknown significance [VUS]) and whether a patient met criteria for genetic testing. RESULTS: A total of 99 patients completed the MICRA survey and 104 completed the family communication survey. The average age of the patients was 67 years, 47% were female, 29% had stage III/IV (AJCC 8th edition) disease, and 42% met genetic testing criteria. Approximately 80% of patients told at least 1 first-degree relative about their result. There was a trend toward greater disclosure among patients who tested positive (93% vs 77% for those with a VUS result [P = .149] and 74% for those who tested negative [P = .069]). Patients not meeting genetic testing criteria were less likely to disclose results (69% vs 93%; P = .003). MICRA scores did not differ by test result, age, stage of disease, or sex. CONCLUSIONS: The rate of result communication was high, although it was lower among patients who did not meet genetic testing criteria, those who tested negative, or those who had a VUS result. Testing-associated distress was similar across patient groups, and was comparable to that reported by other patients with cancer. Improved communication for all patients is crucial given the prognosis of PDAC, which limits time for disclosure.

Prospective study of germline genetic testing in incident cases of pancreatic adenocarcinoma.

BACKGROUND: The objective of this study was to investigate the prevalence of pathogenic germline variants (PGVs) in 32 cancer susceptibility genes in individuals with newly diagnosed pancreatic ductal adenocarcinoma (PDAC). A key secondary objective was to evaluate how often PGVs would have been undetected with existing genetic testing criteria. METHODS: From May 2016 through May 2017, this multicenter cohort study enrolled consecutive patients aged 18 to 89 years with histologically confirmed PDAC diagnosed within the previous 12 weeks. Demographics, medical histories, and 3-generation pedigrees were collected from participants who provided samples for germline DNA analysis. RESULTS: Four hundred nineteen patients were deemed eligible, 302 were enrolled, and 298 were included in the final cohort. Clinically actionable variants were reported in 29 PDAC patients (9.7%), with 23 (7.7%) having a PGV associated with an increased risk for PDAC. Six of 23 individuals (26%) with PDAC-associated gene mutations did not meet currently established genetic testing criteria. According to guideline-based genetic testing, only 11 of the 23 PGVs (48%) in known PDAC genes would have been detected. Six additional patients (2%) had PGVs associated with an increased risk for other cancers. CONCLUSIONS: These findings support the significant prevalence of PGVs associated with PDAC and the limitations of current paradigms for selecting patients for genetic testing, and they thereby lend support for universal germline multigene genetic testing in this population.