Malignant pleural mesothelioma is a malignant neoplasm of mesodermal origin and arises from multipotential mesothelial or subserosal cells of the pleura, pericardium and peritoneum. There are different forms: epitheloid (60%), sarcomatoid (10-20%) and biphasic patterns (20-30%). Metastases to the oral cavity are very rare [1, 2]. They are more common in the jaw bones than the soft tissue. The most common sites for men are the lungs ( 27%), kidneys (13%) and skin (13%) - for women, the breast (24%) and genital organs (17%), followed by bone (10%) and kidney (10%) [1]. The reason for this gender-dependent metastatic pattern has not completely been elucidated yet. In 90% of all pleural mesothelioma, asbestos-association due to occupational exposure is reported. The tumour is found in patients in the fifth and sixth decades. The latency between exposure and manifestation takes approximately 20-40 years. Occurrence of the malignant disease typically carries an average survival rate of 9-12 months [3].
A patient with a history of malignant pleural mesothelioma with metastatic disease to the attached gingiva is presented.
Patient
A 75-year-old man was referred from his private dentist to the Department of Oral Surgery, University of Zurich with a painless growth of the attached gingiva in the disto-buccal region of tooth 35. It had been present for 6 weeks and had increased in size during this period of time.
An epitheloid mesothelioma was diagnosed 2 years earlier (Figure 1) and treated with chemotherapy. The patient commenced the drug Alimta® (Pemetrexed) with palliative intent. He had had a significant asbestos exposure during his working life as an electrician. His medical history was otherwise unremarkable. He was a non-smoker.
Extraorally, neither swelling nor lymphadenopathy was discernible. The innervation of the N.trigeminus was balanced on both sides. Oral examination showed an exophytic, compact and in parts ulcerous swelling surrounding the premolar tooth 35 (Figure 2). The lesion measured approximately 1.5 cm by 1.0 cm. The affected tooth was of grade one mobility, no pathological results in sensitivity and percussion were found and there was no objective paraesthesia in the distribution of the left mental nerve.
Radiological examination (orthopantomogram and digital volume tomography) of the lower jaw revealed no destruction of the bony architecture (Figure 3, 4). There were no changes to the structure of the compacta or spongiosa.
An incisional spindle-shaped biopsy with a thread-mark was carried out under local anaesthesia. The sample measured 10 × 5 mm including both normal and modified gingiva. During the biopsy an unusual blood flow was conspicuous. The second premolar was not extracted.
Histology and immunohistochemistry confirmed the diagnosis of a metastasis of the pleural mesothelioma.
Diagnostic considerations
Clinically, soft tissue metastases typically present as sessile or nodular masses that characteristically resemble hyperplastic reactive lesions, such as pyogenic granuloma or giant cell granuloma [4]. Differential diagnosis, such as other benign tumours of the oral mucosa including lipoma, myxoma, neurofibroma, schwannoma, leiomyoma and various forms of epulis, have to be considered. Murray et al. [5] reported a case where the clinical appearance was most suggestive of a fibroepithelial polyp localized on the dorsum of the tongue. Therefore, excisional biopsy of the lesion was arranged to confirm the diagnosis histologically.
Histology
Grossly, the specimen was a polypous lesion measuring 0,5 × 0,4 cm, protruding from a mucous membrane spindle with a white cut face.
On microscopy, a submucous infiltrate of a neoplasm with marked cell atypia and a glandular growth pattern was seen (Figure 5 & 6).
In comparison, the pleural biopsy taken two years previously, when malignant mesothelioma was originally diagnosed in the patient, showed very similar cytology but a more trabecular architecture with only occasional tubular formations (Figure 7).
Conventional morphology ruled out clinical differential diagnoses such as pyogenic granuloma, epulis, drug-induced gingival hyperplasia or soft tissue tumours.
Likely differentials were metastasis of epitheloid mesothelioma or adenocarcinoma, primarily of the lung.
Calretinin, a mesothelial marker turned out to be strongly positive in tumour cells on immunohistochemical staining (Figure 8), substantiating diagnosis of an epitheloid mesothelioma metastasis. Positive staining for cytokeratins 5/6 and negative staining for Ber-EP4 further helped to distinguish it from adenocarcinoma.