A Case of Three Synchronous Primary Lung Cancers of Distinct Histologies in a Patient With Severe Chronic Obstructive Pulmonary Disease.

Synchronous primary lung cancers are uncommon and present significant diagnostic and therapeutic challenges, particularly when tumors of differing histologies are identified concurrently. Multiple primary lung cancer (MPLC) is defined as the occurrence of two or more distinct primary malignant tumors within the lungs of a single patient, either synchronously or metachronously. Synchronous MPLC requires careful differentiation from intrapulmonary metastases, as misclassification may significantly alter staging and treatment intent. Triple synchronous MPLC is exceptionally rare and is described primarily in isolated case reports and small case series. This case report describes a 65-year-old woman with severe chronic obstructive pulmonary disease (COPD) who was found to have three synchronous primary lung cancers, including limited-stage small cell lung cancer and two distinct non-small cell lung cancers, following evaluation of new pulmonary nodules on surveillance imaging. Comprehensive histopathologic evaluation and multidisciplinary decision-making guided curative-intent concurrent chemoradiation, highlighting the importance of thorough diagnostic sampling and individualized treatment planning in complex presentations. The patient completed therapy but died approximately three months after diagnosis from complications related to advanced COPD and lung malignancy, underscoring the competing mortality risks in this population. This case emphasizes that accurate histologic confirmation of each lesion is essential to ensure appropriate staging under the eighth edition of the tumor, node, metastasis (TNM) classification system and to distinguish synchronous primaries from metastatic disease. Furthermore, coordinated multidisciplinary collaboration among pulmonology, pathology, medical oncology, and radiation oncology is critical to balance oncologic control with preservation of functional status, particularly in patients with severe baseline pulmonary impairment.