Synchronous double primary lung cancers with different response to pemetrexed

Area of Science:

• Oncology
• Pulmonology
• Medical Oncology

Background:

• Synchronous double primary lung cancers present diagnostic challenges, often mimicking metastatic disease.
• Distinguishing between primary lung cancer types is crucial for effective treatment selection.

Observation:

• A 74-year-old male presented with synchronous adenocarcinoma (right lower lobe) and squamous cell carcinoma (left upper lobe) of the lung.
• Initial chemotherapy with pemetrexed and carboplatin showed differential response: right lower lobe mass resolved, while left upper lobe mass progressed.
• Subsequent treatment with S-1 monotherapy led to a decrease in the left upper lobe mass size.

Findings:

• Pemetrexed is effective for non-squamous non-small cell lung cancer but may be less effective or contraindicated with coexisting squamous cell carcinoma.
• The differential response to chemotherapy aided in diagnosing the two distinct primary lung cancers.
• S-1 monotherapy demonstrated efficacy in a pemetrexed-refractory squamous cell lung carcinoma component.

Implications:

• This case suggests S-1 monotherapy as a potential treatment option for pemetrexed-refractory squamous cell lung carcinoma.
• Chemotherapy response patterns can be valuable diagnostic clues in complex lung cancer cases.
• Further research into combination therapies and sequential treatments for synchronous double primary lung cancers is warranted.