Synchronous lung adenocarcinoma and pulmonary carcinoid tumorlets in different lobes: a case report

Background Pulmonary carcinoid tumorlets are small (< 5 mm) neuroendocrine proliferations that are usually identified incidentally in resected lung tissue. Their coexistence with a spatially separate lung adenocarcinoma is uncommon and may complicate the interpretation of multiple pulmonary nodules. Case summary A 71-year-old woman with multiple bilateral pulmonary micronodules that had remained radiologically stable for approximately 2 years was admitted after a newly detected lesion in the apicoposterior segment of the left upper lobe was considered suspicious for lung cancer. She reported occasional chest tightness and intermittent cough with sputum and had never smoked. Bronchoscopy and brush cytology were negative. The patient underwent video-assisted thoracoscopic wedge resection of the left upper lobe lesion. Frozen-section examination showed adenocarcinoma, prompting a left upper lobectomy with systematic lymph-node dissection. A left lower lobe wedge resection was performed to sample representative micronodules. Final pathology showed a 3.0-cm invasive adenocarcinoma (approximately 80% acinar and 20% lepidic patterns), without visceral pleural, definite vascular invasion, or metastasis in 17 sampled lymph nodes (pT1cN0M0, stage IA3). The left lower lobe nodules were reported as pulmonary carcinoid tumorlets and were positive for AE1/AE3, synaptophysin, chromogranin A, CD56, and TTF-1, with a Ki-67 index of approximately 2%. The adenocarcinoma harbored an EGFR exon 21 L858R mutation. She was discharged 1 week after surgery. Conclusion This case illustrates that pulmonary micronodules accompanying a dominant lung cancer may represent a separate neuroendocrine proliferation rather than intrapulmonary metastases. Diagnosis requires correlation of lesion size, morphology, and immunophenotype. Unsampled contralateral nodules could remain radiologically indeterminate and undergo structured surveillance.