A case of multiple pulmonary metastasizing pleomorphic adenomas of the salivary gland.

To the Editor: As the most common benign neoplasm of the salivary gland, pleomorphic adenoma is characterized by slow progression and low morbidity.[ It is quite rare for the pleomorphic adenoma to metastasize before undergoing malignant transformation, resulting in that there is no clear consensus about the epidemiology, mechanism of development, treatment, and prognosis of metastasizing pleomorphic adenomas (MPA).[ According to the systematic review study of James Knight, 72.8% of cases reported pleomorphic adenoma (PA) local recurrence before MPA. MPA usually spread to the bone (36.6%), the lung (33.8%), and neck lymph nodes (20.1%).[ The case we reported was the pulmonary MPA of the salivary gland.

A 25-year-old man presented with the finding of multiple bilateral well-defined non-calcified nodular lesions in the lung on his computed tomography (CT) for the pre-operative examination due to the second recurrence of PA of the right parotid gland. He was diagnosed as PA of the right parotid gland at the age of 16 years and underwent a local mass resection. The PA recrudesced after 2 years, and he had to accept the right parotid mass resection and facial nerve anatomy. After another 5 years, the patient felt and touched multiple mung-bean-like granular nodules on the right side of the face and neck. As nodules grew as the time goes, he had to receive enlarged resection of the right parotid PA, facial nerve anatomy, and tissue patch implantation. After the operation, the patient was presented to our hospital with the abnormal finding on CT. He has no symptom of the respiratory system and no decreased exercise tolerance all the time. The F-18 fluorodeoxyglucose positron emission tomography (FDG-PET)/CT showed that the multiple nodules in the lungs have a low intake of FDG, which, to some extent, suggests the characteristics of benign neoplasm [Figure 1]. Subsequent pathological results of needle biopsy also confirmed it. The microscopy presented a mixture of spindle tumor cells on the background of mucoid and cartilage-like components, which was the typical performance of PA. Further immunohistochemistry results showed tumor protein p63 (+), cytokeratin5/6 (+), cytokeratin7 (+), smooth muscle actin, (+), soluble protein-100 (+), cytokeratin (+), and antigen KI67 (−).

Figure 1

FDG-PET/CT of this patient. There are multiple bilateral well-defined round nodules with mild or slight FDG ingestion in the lung. The diameter of large ones is about 1.2 cm × 1.1 cm in lung window and 0.9 cm × 0.7 cm in mediastinum window. Standardized uptake value (SUV) max is 2.2. No enlarged lymph nodes and imaging agent abnormal concentration in the bilateral hila. It showed no abnormal uptake in pulmonary metastasizing lesions. FDG-PET/CT: F-18 fluorodeoxyglucose positron emission tomography/computed tomography; SUV: Standardized uptake value.

For the local PA, surgical resection usually is the first choice with no controversy, but sometimes enucleation may prompt recurrence, which necessitates enlarged resection. But when PA grow progressively to MPA, there is no consensus about the management to the primary lesion and the metastatic lesion. It is hard to remove the multiple pulmonary metastatic lesions by surgical resection. Histologically benign and low proliferative properties do not support chemotherapy. In our case, FDG-PET/CT showed no abnormally high uptake in pulmonary metastasizing lesions, which did not embrace the choice of chemotherapy. Some cases reported the effectiveness of chemotherapy to carcinoma ex-pleomorphic adenoma (CEPA).[ Though the MPA has benign histology yet malignant behavior, sometimes it is classified as a kind of malignant PA, which includes three forms: CEPA, carcinosarcoma, and MPA. Radiotherapy is often regarded as an auxiliary means of preventing recurrence after surgery and not recommended for an isolated primary lesion and is not necessarily indicated for an isolated recurrence in a younger patient.[ It seems that the local recurrence is greatly related to the MPA. Lacking study about the prognosis of MPA, we just know the presence of multiple metastases is an independent negative prognostic factor. However, there is something different from our case in the uptake of FDG and mixed tumor component in most cases reported. Based on the patient's surgery history, we speculated that the reason of multiple pulmonary MPA is the surgical manipulation. The management of benign MPA is challenging on the condition that the patient is asymptomatic and the lesions are multiple and low proliferative. The cases reported also usually took a necessary long-term follow-up without a better choice. We also will do a prolonged follow-up of the patient and look for more evidence in the management of MPA.

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Conflicts of interest

None.