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Difficulty: Very hardNeoplastic Processes

A 6262-year-old woman is evaluated in the oncology clinic for progressive shortness of breath and right upper quadrant abdominal fullness over the past three weeks. She has a history of metastatic non-small cell lung cancer (NSCLC) diagnosed 2020 months ago. At the time of initial diagnosis, molecular testing of the lung primary tumor revealed an epidermal growth factor receptor (EGFR) exon 1919 deletion. She was started on osimertinib, with a robust partial response. She has no other significant past medical history and has never smoked. Current vital signs are within normal limits.

Physical examination reveals decreased breath sounds at the right lung base and a palpable, slightly tender liver edge 44 cm below the right costal margin. Restaging computed tomography (CT) of the chest, abdomen, and pelvis demonstrates enlargement of the primary right lung mass, new right-sided pleural effusion, and multiple new, hypervascular hepatic lesions.

A liquid biopsy (cell-free DNA) is performed and confirms the presence of the original EGFR exon 1919 deletion but is negative for secondary EGFR mutations, including T790M and C797S, as well as MET amplification. Subsequently, an ultrasound-guided core needle biopsy of one of the new hepatic lesions is performed. Histopathologic evaluation of the liver specimen reveals sheets of small cells with scant cytoplasm, finely granular nuclear chromatin, and absent glandular architecture. Immunohistochemical staining is strongly positive for synaptophysin and chromogranin A.

Based on the patient's new clinicopathologic findings, which of the following is the most appropriate next step in management?

  1. Initiate combination therapy with etoposide and a platinum agentAnswer
  2. B
    Discontinue current therapy and initiate an alternative epidermal growth factor receptor inhibitor
  3. C
    Continue current therapy and obtain an image-guided core biopsy of the enlarging primary lung mass
  4. D
    Order next-generation sequencing on the original archived lung tumor tissue
  5. E
    Add a programmed death-ligand 1 inhibitor to the patient's current targeted therapy regimen

Answer

Initiate combination therapy with etoposide and a platinum agent
The correct answer is to initiate combination therapy with etoposide and a platinum agent. This patient with EGFR-mutated lung adenocarcinoma has developed acquired resistance to the third-generation EGFR inhibitor, osimertinib. While acquired secondary kinase domain mutations (such as C797S) and bypass track signaling (such as MET amplification) are common resistance mechanisms, approximately 3%3\% to 15%15\% of EGFR-mutated NSCLCs undergo lineage plasticity and transform into small cell lung cancer (SCLC). The recent liver biopsy exhibits classic SCLC histology: solid sheets of cells with scant cytoplasm, finely granular chromatin, absent glandular architecture, and positive staining for neuroendocrine markers (synaptophysin, chromogranin A). The original EGFR mutation is typically retained, as seen in this patient's cell-free DNA. Once histologic transformation to SCLC is confirmed, the tumor behaves clinically like primary SCLC. Therefore, standard-of-care management must pivot to an SCLC-directed cytotoxic chemotherapy regimen, typically a platinum agent combined with etoposide.

Step-by-Step Solution

1
Analyze the patient's initial diagnosis and current therapy.
The patient has EGFR-mutated NSCLC and has been receiving osimertinib for 2020 months.
Establishing the baseline molecular profile is essential to understanding potential acquired resistance mechanisms.
2
Interpret the new biopsy findings from the progressing hepatic lesion.
The biopsy shows sheets of small cells, granular chromatin, and positivity for synaptophysin and chromogranin A, confirming neuroendocrine differentiation.
Identifying the precise histologic changes explains the clinical progression despite ongoing targeted therapy.
3
Synthesize the clinical history and pathology to determine the resistance mechanism.
The findings indicate histologic transformation from adenocarcinoma to small cell lung cancer (SCLC).
Accurate characterization of the tumor's new biology dictates the subsequent treatment strategy.
4
Determine the standard of care management for the newly identified tumor histology.
The appropriate treatment for extensive-stage SCLC is cytotoxic chemotherapy with a platinum agent and etoposide.
The tumor is no longer solely dependent on the EGFR pathway; therefore, EGFR inhibitors are insufficient, and SCLC requires aggressive chemotherapy.

Key Concept

Histologic transformation to small cell lung cancer (SCLC) is a known mechanism of acquired resistance to EGFR tyrosine kinase inhibitors in NSCLC, presenting with neuroendocrine morphology and requiring a shift to SCLC-directed chemotherapy.
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Topics

Neoplastic Processes

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