Background. We report 2 cases of collision cancer of the lung. Case. Case 1: A 70-year-old woman complained of cough, and was referred to our hospital. A chest computed tomography (CT) scan showed a mass 6.0 x 3.2 cm in size in the right lower lobe. Bronchoscopic examination revealed squamous cell carcinoma in the right truncus intermedius. A right middle and lower sleeve lobectomy was successfully performed. The histopathological diagnosis was a collision tumor with components of small cell carcinoma and squamous cell carcinoma. The patient underwent adjuvant chemotherapy with CDDP and VP-16, and is alive with no evidence of recurrence 3 years and 6 months after surgery. Case 2: An abnormal shadow in the right upper lobe of the lung was detected in a 70-year-old woman, 1 year after a left lingular segmentectomy due to large cell carcinoma. A chest CT scan showed a nodular lesion measuring 2.0 x 1.5 cm in maximum dimension. For definitive diagnosis and treatment a right upper lobectomy was performed. Pathologically the lesion was diagnosed as a collision tumor with components of adenocarcinoma and squamous cell carcinoma. The patient was followed up as an outpatient without any evidence of recurrence, but died of acute myocardial infarction 6 months after surgery. Conclusion. Pulmonary collision cancer of the lung is relatively rare, and preoperative diagnosis is often difficult. The treatment strategy should be based on the biological behavior and pathological stage of each individual cancer component.
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