Pulmonary langerhans cell histiocytosis following resection of lung adenocarcinoma: a case report and diagnostic challenges.

Pulmonary Langerhans cell histiocytosis (PLCH) is an uncommon myeloid disorder of the lung characterized by the accumulation of Langerhans-like cells within the pulmonary parenchyma. On imaging, it typically presents as nodular or cystic lesions and is closely associated with cigarette smoking. Although PLCH can occur in both children and adults, it is more frequently observed in younger smokers and is relatively rare in elderly individuals. In most cases, the disease follows a slow and sometimes self-limiting course, and systemic therapy is not routinely required. However, radiologic differentiation from malignant ground-glass nodules may be challenging. The development of PLCH after lung adenocarcinoma surgery is rare. Here, we report the case of a 72-year-old woman with lung adenocarcinoma. Following resection of a right lung nodule, molecular testing identified an EGFR exon 19 deletion, and icotinib was subsequently administered for contralateral ground-glass nodules. During postoperative follow-up, new lesions were detected in the rib adjacent to the surgical field as well as in the lung, raising concern for possible bone metastasis on imaging. Percutaneous biopsy with immunohistochemical analysis demonstrated positivity for CD1a, Langerin, and S-100, while lung adenocarcinoma-associated markers, including CK7, TTF-1, and Napsin A, were negative, supporting a diagnosis of PLCH. The next generation sequencing found BRAF V600E mutation in PLCH lesions. After symptomatic treatment and long-term follow-up, the lesions gradually improved and partially disappeared. Looking back on the previously reported cases, it is not common for PLCH and lung adenocarcinoma to coexist. In published reports, these two conditions generally have different driving gene changes, and their potential biological relationship is still unclear. This case shows that when new lesions are found after lung cancer surgery, besides tumor recurrence, other diagnoses, namely PLCH, should be considered, and the diagnosis should be confirmed by histopathological examination.