Somatic Tumor Testing Implications for Lynch Syndrome Germline Genetic Testing

Deficiencies in germline genetic testing in young-onset colorectal cancer patients

BACKGROUND

Young-onset colorectal cancer (YO-CRC) patients have high rates of pathologic genetic variants on germline testing, however it is unclear what factors are associated with genetic testing completion.

METHODS

We performed a retrospective review of YO-CRC patients aged ≤50 years between 2014 and 2021 who received the entirety of their cancer care at a single institution. The primary outcome was completion of germline multigene panel testing. Variables were examined for association with germline multigene panel testing.

RESULTS

Among 100 YO-CRC patients, only 31 ​% (n ​= ​31) completed genetic testing. Testing rates did not differ by colorectal cancer stage but were significantly higher among patients who received chemotherapy (39.8 ​% vs 5.9 ​%; p ​= ​0.01) and in patients with increasing number of relatives with a family history of cancer (p ​< ​0.01).

CONCLUSIONS

Only one-third of YO-CRC patients completed genetic testing. Patients seen by oncology or with increasingly strong family cancer history were more likely to complete genetic testing.

Preventive strategies in familial and hereditary colorectal cancer

Colorectal cancer is a leading cause of cancer-related deaths worldwide. While most cases are sporadic, a significant proportion of cases are associated with familial and hereditary syndromes. Individuals with a family history of colorectal cancer have an increased risk of developing the disease, and those with hereditary syndromes such as Lynch syndrome or familial adenomatous polyposis have a significantly higher risk. In these populations, preventive strategies are critical for reducing the incidence and mortality of colorectal cancer. This review provides an overview of current preventive strategies for individuals at increased risk of colorectal cancer due to familial or hereditary factors. The manuscript includes a discussion of risk assessment and genetic testing, highlighting the importance of identifying at-risk individuals and families. This review describes various preventive measures, including surveillance colonoscopy, chemoprevention, and prophylactic surgery, and their respective benefits and limitations. Together, this work highlights the importance of preventive strategies in familial and hereditary colorectal cancer.

Somatic tumor mutations in moderate risk cancer genes: Targets for germline confirmatory testing

BACKGROUND

Recent changes in oncology practice guidelines indicate that mutations in cancer susceptibility genes identified on tumor genomic profiling (TGP) should prompt confirmatory germline testing. Our study aimed to determine the proportion of patients with TGP-identified mutations in moderate risk breast and ovarian cancer genes who previously would not have been considered for germline testing.

METHODS

From January 2013 to September 2020, 7468 adult Stanford Health Care patients underwent TGP on solid tumor samples and 166 had TGP-identified mutations in moderate risk breast and ovarian cancer susceptibility genes (ATM, BRIP1, CHEK2, PALB2, RAD51C and RAD51D). Retrospective chart reviews were performed on 160 patients. Cases were analyzed to determine eligibility for germline testing using established NCCN criteria, and somatic and germline results were compared where both were available.

RESULTS

Nearly half (45.3% [73/160]) of patients would not have been eligible for germline testing if not for a TGP-identified mutation in a moderate risk breast or ovarian cancer gene. Of the 64 cases that underwent germline testing, about half (51.5% [33/64]) had results that confirmed germline origin of the TGP finding. High rates of germline confirmation were found in PALB2 (100% [5/5]), ATM (40% [14/35]), CHEK2 (61.5% [8/13]), and BRIP1 (57.1% [4/7]).

CONCLUSION

Our study shows that the presence of TGP-identified mutations in moderate risk breast and ovarian cancer genes increases eligibility for germline testing beyond those that would be eligible based largely on personal and family history criteria alone. Additionally, results of germline testing in these newly eligible cases supports that this expanded eligibility captures individuals with hereditary cancer syndromes that would not have otherwise been identified.