From 7% to nearly 9% of patients with advanced cancer were found to harbor a germline variant with targeted therapeutic actionability in the first study of its kind.
The study involved 11,974 patients with various tumor types. All the patients underwent germline genetic testing from 2015 to 2019 at the Memorial Sloan Kettering Cancer Center (MSKCC) in New York City, using the next-generation sequencing panel MSK-IMPACT.
This testing identified 2043 patients (17.1%) with variants in cancer predisposition genes, including 849 patients (7.1%) who had targetable genes by strict criteria and 1003 patients (8.6%) by less strict criteria.
"Of course, these numbers are not static," commented lead author Zsofia K. Stadler, MD, a medical oncologist at MSKCC. "And with the emergence of novel targeted treatments with new FDA indications, the therapeutic actionability of germline variants is likely to increase over time.
"Our study demonstrates the first comprehensive assessment of the clinical utility of germline alterations for therapeutic actionability in a population of patients with advanced cancer," she added.
Stadler presented the study results during a virtual scientific program of the American Society of Clinical Oncology (ASCO) 2020.
Testing for somatic mutations is evolving as the standard of care in many cancer types, and somatic genomic testing is rapidly becoming an integral part of the regimen for patients with advanced disease. Some studies suggest that 9% to 11% of patients harbor actionable genetic alterations, as determined on the basis of tumor profiling.
"The take-home message from this is that now, more than ever before, germline testing is indicated for the selection of cancer treatment," said Erin Wysong Hofstatter, MD, from the Yale School of Medicine, New Haven, Connecticut, in a Highlights of the Day session.
Now, more than ever before, germline testing is indicated for the selection of cancer treatment. Dr Erin Wysong Hofstatter
An emerging indication for germline testing is the selection of treatment in the advanced setting, she noted. "And it is important to know your test. Remember that tumor sequencing is not a substitute for comprehensive germline testing."
Implications in Cancer Treatment
For their study, Stadler and colleagues reviewed the medical records of patients with likely pathogenic/pathogenic germline (LP/P) alterations in genes that had known therapeutic targets so as to identify germline-targeted treatment either in a clinical or research setting.
"Since 2015, patients undergoing MSK-IMPACT may also choose to provide additional consent for secondary germline genetic analysis, wherein up to 88 genes known to be associated with cancer predisposition are analyzed," she said. "Likely pathogenic and pathogenic germline alterations identified are disclosed to the patient and treating physician via the Clinical Genetic Service."
A total of 2043 (17.1%) patients who harbored LP/P variants in a cancer predisposition gene were identified. Of these, 11% of patients harbored pathogenic alterations in high or moderate penetrance cancer predisposition genes. When the analysis was limited to genes with targeted therapeutic actionability, or what the authors defined as tier 1 and tier 2 genes, 7.1% of patients harbored a targetable pathogenic germline alteration.
BRCA alterations accounted for half (52%) of the findings, and 20% were associated with Lynch syndrome.
The tier 2 genes, which included PALB2, ATM, RAD51C, and RAD51D, accounted for about a quarter of the findings. Hofstatter noted that, using strict criteria, 7.1% of patients were found to harbor a pathogenic alteration and a targetable gene. Using less stringent criteria, additional tier 3 genes and additional genes associated with DNA homologous recombination repair brought the number up to 8.6%.
Therapeutic Action
For determining therapeutic actionability, the strict criteria were used; 593 patients (4.95%) with recurrent or metastatic disease were identified. For these patients, consideration of a targeted therapy, either as part of standard care or as part of an investigation or research protocol, was important.
Of this group, 44% received therapy targeting the germline alteration. Regarding specific genes, 50% of BRCA1/2 carriers and 58% of Lynch syndrome patients received targeted treatment. With respect to tier 2 genes, 40% of patients with PALB2, 19% with ATM, and 37% with RAD51C or 51D received a PARP inhibitor.
Among patients with a BRCA1/2 mutation who received a PARP inhibitor, 55.1% had breast or ovarian cancer, and 44.8% had other tumor types, including pancreas, prostate, bile duct, gastric cancers. These patients received the drug in a research setting.
For patients with PALB2 alterations who received PARP inhibitors, 53.3% had breast or pancreas cancer, and 46.7% had cancer of the prostate, ovary, or an unknown primary.
Looking Ahead
The discussant for the paper, Funda Meric-Bernstam, MD, chair of the Department of Investigational Cancer Therapeutics at the University of Texas MD Anderson Cancer Center, Houston, pointed out that most of the BRCA-positive patients had cancers traditionally associated with the mutation. "There were no patients with PTEN mutations treated, and interestingly, no patients with NF1 were treated," she said. "But actionability is evolving, as the MEK inhibitor selumitinib was recently approved for NF1."
Some questions remain unanswered, she noted, such as, "What percentage of patients undergoing tumor-normal testing signed a germline protocol?" and, "Does the population introduce a bias — such as younger patients, family history, and so on?"
It is also unknown what percentage of germline alterations were known in comparison with those identified through tumor/normal testing. Also of importance is the fact that in this study, the results of germline testing were delivered in an academic setting, she emphasized. "What if they were delivered elsewhere? What would be the impact of identifying these alterations in an environment with less access to trials?
"But to be fair, it is not easy to seek the germline mutations," Meric-Bernstam continued. "These studies were done under institutional review board protocols, and it is important to note that most profiling is done as standard of care without consenting and soliciting patient preference on the return of germline results."
An infrastructure is needed to return/counsel/offer cascade testing, and "analyses need to be facilitated to ensure that findings can be acted upon in a timely fashion," she added.
The study was supported by MSKCC internal funding. Stadler reports relationships (institutional) with Adverum, Alimera Sciences, Allergan, Biomarin, Fortress Biotech, Genentech/Roche, Novartis, Optos, Regeneron, Regenxbio, and Spark Therapeutics. Meric-Bernstram reports relationships with numerous pharmaceutical companies.
American Society of Clinical Oncology (ASCO) 2020: Abstract 1500, presented May 30, 2020.
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