Detection of EGFR T790M in a Large Amount of Malignant Ascites Cellblock

Area of Science:

• Oncology
• Molecular Diagnostics
• Genetics

Background:

• Lung adenocarcinoma treatment often involves epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs).
• Acquired resistance to first- and second-generation EGFR TKIs commonly arises from the EGFR T790M mutation.
• Standard diagnostic methods for resistance mutations include repeat tissue biopsy.

Observation:

• A patient with EGFR exon 19 deletion-mutated lung adenocarcinoma developed malignant ascites and pleural effusion during erlotinib and afatinib treatment.
• Initial examinations of pleural and ascitic fluids failed to detect the EGFR T790M mutation.
• Subsequent analysis of a larger volume of ascitic fluid via cellblock successfully identified the EGFR exon 20 T790M mutation.

Findings:

• The presence of the EGFR exon 20 T790M mutation in ascitic fluid was confirmed.
• Treatment with osimertinib, an EGFR TKI targeting the T790M mutation, led to significant reduction in ascites and primary tumor burden.
• Osimertinib demonstrated high efficacy in managing lung cancer progression driven by the T790M mutation.

Implications:

• Ascitic fluid examination can serve as a viable alternative to tissue biopsy for detecting EGFR T790M mutations in lung cancer.
• This approach facilitates timely diagnosis and initiation of appropriate targeted therapy, such as with osimertinib.
• Liquid biopsy in malignant effusions offers a minimally invasive strategy for guiding treatment decisions in advanced lung adenocarcinoma.