Primary salivary gland-type polymorphous adenocarcinoma in the lung A case report and literature review

Rationale: Polymorphous low-grade adenocarcinoma is a low-risk infiltrative malignant tumor of the salivary glands. However, some of these tumors are more malignant than the low-grade tumors and therefore, according to the most recent recommendation of the World Health Organization, they are renamed as polymorphous adenocarcinomas (PACs). Primary polymorphous low-grade adenocarcinomas/PACs of the lungs are rare. Herein, we report a case of primary PAC of the lung with bronchial cartilage and perineural invasion, and lymph node metastasis. Patient concerns: A 58-year-old man had developed fever half a month prior, without chills or other accompanying symptoms, and the underlying reasons were unknown. His self-measured temperature was up to 39 degrees C, accompanied by cough and expectoration, yellow and thin sputum, and shortness of breath. The patient's general state was normal, and respiratory sounds originating from the right lung were weak. Enhancement computed tomography revealed that the bronchial lumen of the basal segment of the lower lobe of the right lung was narrow; soft tissue density nodules were seen, with a range of approximately 2.4 cm x 1.3 cm. Diagnosis: Based on clinical information, morphological features, and immunohistochemistry results, the pathological diagnosis was primary PAC of the lungs. Intervention: Thoracoscopic resection of the middle and lower lobes of the right lung was performed, further extended dissection of the mediastinal lymph nodes was performed. Outcomes: The postoperative course was uneventful. Lessons: Primary PAC of the lung is rare and may cause misdiagnosis. When encountering a lung tumor with diverse tissue structures, uniform cell type and nerve invasion, we should consider the possibility of PAC. Morphological and immunohistochemical features can be useful for diagnosing primary PAC of the lungs.