Combined Small and Squamous Transformation in EGFR-mutated Lung Adenocarcinoma

Area of Science:

• Oncology
• Molecular Biology
• Cancer Research

Background:

• Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are standard treatment for EGFR-mutated lung adenocarcinoma.
• Acquired resistance to EGFR-TKIs is a significant clinical challenge.
• Histologic transformation is a known, but incompletely understood, mechanism of acquired resistance.

Observation:

• A patient with stage IV lung adenocarcinoma and EGFR exon 19 deletions was treated with EGFR-TKIs.
• Resistance developed, necessitating treatment with cytotoxic chemotherapy.
• A lymph node re-biopsy demonstrated transformation to a combined small-cell lung cancer and squamous cell carcinoma histology.
• EGFR exon 19 deletions were retained in the transformed tumor cells.

Findings:

• Histologic transformation to combined small-cell and squamous cell carcinoma occurred despite retained EGFR exon 19 deletions.
• The transformed tumor exhibited sensitivity to sequential chemotherapy regimens tailored to the new histology.
• A clinical response was achieved following treatment for the transformed histology.

Implications:

• Histologic transformation should be considered in patients with EGFR-mutated lung cancer who develop acquired resistance to TKIs.
• Re-biopsy and molecular testing are crucial for identifying transformation and guiding subsequent treatment.
• Chemotherapy regimens appropriate for the transformed histology can be effective.
• Understanding resistance mechanisms like histologic transformation is key to improving lung cancer treatment outcomes.