Clinical conundrums: Developing a strategy for discerning TP53-associated chip and coherent clinical care

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Background: Germline TP53 mutations are associated with Li-Fraumeni syndrome (LFS). However, approximately 20% of commercial laboratory multigene panel test (MGPT)-detected pathogenic TP53 variants represent aberrant clonal expansion (ACE), rather than a germline finding, and are often detected in individuals that lack classic features of LFS. Clonal hematopoiesis (CH) is a form of ACE, and in the absence of an abnormal hemogram is termed Clonal hematopoiesis of indeterminate potential (CHIP). CHIP is often associated with a pathogenic variant (PV) in hematopoietic pathway gene(s) at a variant allele frequency (VAF) less than expected for a heterozygous germline finding. The prevalence increases with age and exposure to chemotherapy. The presence of a skewed VAF is usually noted in a comment on a genetic test result, however, clinicians without genetic training often lack understanding of the comment and need strategies to discern the difference between germline findings, CHIP, and post-zygotic mosaicism. Our studies illuminate possible strategies for discernment for clinicians. Methods: Among 113 cases with MGPT-detected TP53 PVs, enrolled in the Clinical Cancer Genomics Community Research Network registry, we obtained additional tissues, family history and complete blood count (CBC) reports on 42 cases. DNA extracted from formalin fixed paraffin embedded (FFPE) tumor/normal tissues, blood, saliva, eyebrow plucks, was analyzed using a previously validated custom myeloid and CH gene (n = 79) amplicon-based QIAseq panel. PVs with VAF > 2% were included in analyses. Results: Germline status was confirmed for 6 cases (one with a CH PV), post-zygotic mosaicism was supported for 5 cases and 2 were indeterminant. 12 had results supporting ACE/CH, with additional CH-associated PV(s) identified in 5/12 (41%); n = 2 of each TET2, ATM, TP53; and increasing VAF over time for the driver TP53 PV was noted in 2. Of these 2 one was identified to have a hematopoietic malignancy identified through analysis of the CBCs and bone marrow biopsy in parallel with the increasing VAF. Additional results are pending for 7 cases. Conclusions: With the use of our multi-tissue NGS strategy, serial sampling of suspected ACE/CH cases, family history and CBC analyses we were able to discern the status of most TP53 genetic findings. This work has direct translational impact, refining risk estimation and improving the clinical care of patients with TP53 PVs, while avoiding unnecessary LFS-related care and enabling appropriate care for those with ACE.

Effect of germline ATM mutations on clonal hematopoiesis

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Background: Clonal hematopoiesis (CH) in myeloid related-genes is associated with development of primary and secondary leukemia and atherosclerotic disease, as well as, decreased overall survival. Identification of factors beyond age and cytotoxic exposures that predispose to CH may be useful to both recognize individuals at increased risk for CH and to better understand how CH develops. We have previously shown that germline mutations in the DNA repair gene ATM may predispose to CH. We hypothesized here that heterozygous ATM germline mutation carriers would have higher rates of CH in myeloid genes compared to controls. Methods: Germline DNA samples from 34 heterozygous ATM germline mutation carriers (cases) and 22 controls without ATM germline mutations were sequenced on an Illumina 2500 using a custom 79-gene-myeloid-CH-coding-exon-amplicon-based Qiaseq panel. Read depth averaged 130x. Pathogenic and likely pathogenic CH variants (PV) above an allele fraction of 2% were used for analyses. Cases and controls were compared using a rank-sum test. Results: Cases had a higher median age (56 years, range 30-82) than controls (48 years, range 5-72). Cases and controls were similar in solid tumor cancer history and known exposure to cancer cytotoxic therapy; 73.5% vs 86.4%, and 18.1 vs 20.6%, respectively. The number of CH PV was similarly associated with age in both cases and controls (cor = 0.31, p = 0.01). Cases displayed more CH PVs than controls (total 62 vs 3 PVs, median 2 PVs vs 0, p = 10-6). Of note, cases frequently had a concomitant second (n = 10; 29% of cases) or third (n = 4; 11.8% of cases) unique ATM CH PV, whereas no ATM CH PVs were seen in controls. Even after excluding ATM CH PVs, CH PVs were more frequent in cases (p = 0.00003). After ATM CH PVs, the most frequent CH PVs in cases were in NF1 (5 PVs), BCORL1 (4 PVs), and DMNT3A (4 PVs). Conclusions: Our study supports ATM as a strong predisposition locus for myeloid gene CH. CH in ATM germline mutation carriers frequently involved unique low allele fraction PVs in ATM, suggesting ATM germline PVs are driving production of likely bi-allelic ATM inactivation in white blood cells, or complete ATM loss. Complete ATM loss may be a nidus particularly for lymphocytic leukemia, as bi-allelic ATM inactivation is a frequent somatic finding.

Identification of Incidental Germline Mutations in Patients With Advanced Solid Tumors Who Underwent Cell-Free Circulating Tumor DNA Sequencing

PURPOSE

To determine the potential for detection of incidental germline cancer predisposition mutations through cell-free DNA (cfDNA) analyses in patients who underwent solid tumor somatic mutation evaluation.

PATIENTS AND METHODS

Data were evaluated from 10,888 unselected patients with advanced (stage III/IV) cancer who underwent Guardant360 testing between November 2015 and December 2016. The main outcome was prevalence of putative germline mutations identified among 16 actionable hereditary cancer predisposition genes.

RESULTS

More than 50 cancer types were studied, including lung (41%), breast (19%), colorectal (8%), prostate (6%), pancreatic (3%), and ovarian (2%). Average patient age was 63.5 years (range, 18 to 95 years); 43% were male. One hundred and fifty-six individuals (1.4%) had suspected hereditary cancer mutations in 11 genes. Putative germline mutations were more frequent in individuals younger than 50 years versus those 50 years and older (3.0% v 1.2%, respectively; P < .001). Highest yields of putative germline findings were in patients with ovarian (8.13%), prostate (3.46%), pancreatic (3.34%), and breast (2.2%) cancer. Putative germline mutation identification was consistent among 12 individuals with multiple samples. Patients with circulating tumor DNA copy number variation and/or reversion mutations suggestive of functional loss of the wild-type allele in the tumor DNA also are described.

CONCLUSION

Detection of putative germline mutations from cfDNA is feasible across multiple genes and cancer types without prior mutation knowledge. Many mutations were found in cancers without clear guidelines for hereditary cancer genetic counseling/testing. Given the clinical significance of identifying hereditary cancer predisposition for patients and their families as well as targetable germline alterations such as in BRCA1 or BRCA2, research on the best way to validate and return potential germline results from cfDNA analysis to clinicians and patients is needed.

Graduates' evaluation of a postgraduate diploma course in family medicine

BACKGROUND

Postgraduate programmes offer an opportunity to learn family medicine for physicians in practice who were unable to obtain formal training in the immediate postgraduate phase of their career. Since 1985, the Chinese University of Hong Kong has provided a part-time 1-year diploma course at hours convenient for private practitioners. The curriculum has evolved, reducing public health components and increasing family medicine concepts. Between six and 16 students took the course each year until 1999, when formal recognition led to increased popularity.

OBJECTIVE

The aim of this study was to evaluate the components and outcomes of the course as a prelude to further development.

METHODS

Evaluation comprised a structured telephone interview conducted with two enrollees from each year of the course (total 28), selected randomly from class lists.

RESULTS

Participants were mostly young doctors, with an average of 5 years in general practice. Many graduates are now prominent in training and development of family medicine in Hong Kong. Graduates rated most components favourably, but found the original research components too demanding, and not useful subsequently for most. Counselling, family dynamics, consultation and practice organization skills were valued. Conventional continuing education components, such as lectures by specialists, were evaluated poorly.

CONCLUSIONS

This course has proved useful in the Hong Kong context, being practical for physicians, and allowing them to study ideas they would not otherwise encounter. Critical appraisal and evidence-based medicine exercises now replace the former research components.