Diagnostic and Therapeutic Challenges in an Older Patient With Concurrent Small-Cell Lung Carcinoma and Primary Duodenal Adenocarcinoma: A Case Report

An 80-year-old woman presented with weight loss, elevated pro-gastrin-releasing peptide levels, and later developed exertional dyspnea. Contrast computed tomography of the chest revealed multiple masses in the left upper lobe of the lung, left hilar and mediastinal lymphadenopathy, and pleural effusion, suggesting pleural dissemination. Additionally, positron emission tomography-computed tomography showed fluorodeoxyglucose uptake in the descending portion of the duodenum and associated wall thickening. Histopathological examination of the bronchoscopic biopsy specimens demonstrated small to intermediate-sized tumor cells with scant cytoplasm, finely granular chromatin, and nuclear molding, supporting the diagnosis of small-cell lung cancer (SCLC). She was diagnosed with extensive-stage SCLC and experienced gastrointestinal bleeding from the suspected duodenal metastasis lesion before the treatment, with severe anemia. She was promptly started on systemic chemotherapy with carboplatin, etoposide, and durvalumab due to clinical urgency and suspicion of duodenal metastasis. Although the pulmonary tumor responded to treatment, gastrointestinal bleeding persisted. The endoscopic biopsy confirmed primary duodenal adenocarcinoma. Surgical resection was not pursued due to the patient's condition, and chemotherapy for SCLC was continued. This case illustrates the importance of synchronous primary cancers in patients with atypical presentations and highlights the need to balance prompt treatment with thorough diagnostic evaluation. Early treatment of the more aggressive cancer allowed clinical stabilization and outpatient management, demonstrating a pragmatic approach to complex oncologic care in elderly patients.