[Abnormally Elevated Procalcitonin in Stage IV Lung Adenocarcinoma 
with Neuroendocrine Differentiation: A Case Report and Literature Review].

Procalcitonin (PCT) is a key biomarker widely used in clinical practice for the diagnosis of bacterial infection, assessment of antimicrobial efficacy, and prognostic evaluation. Studies have shown that PCT can also be elevated in various malignancies, correlating closely with tumor progression, metastasis, and poor prognosis. However, the value of PCT in monitoring disease status and treatment response in non-small cell lung cancer (NSCLC) remains unclear. This article reports a case of a patient with previously treated stage IV lung adenocarcinoma with neuroendocrine differentiation, who presented with a marked elevation in serum PCT in the absence of active infection. Following local radiotherapy to the pleural metastatic lesion, the PCT level declined rapidly. This report aims to explore the potential clinical significance of PCT in NSCLC with neuroendocrine differentiation and to provide a reference for disease assessment and prognostic evaluation in patients with similar symptoms.
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