A case report of metastasis of malignant mesothelioma to the retromolar trigone

Malignant mesothelioma is a rare and aggressive tumor with a poor prognosis. The incidence of this disease is one or two cases per million per year [7]. The diagnosis of the primary malignant mesothelioma is established by clinical, histological, immunohistochemical, and radiological findings. In the present report, calretinin, a mesothelial marker turned out to be strongly positive in tumour cells on immunohistochemical staining, substantiating diagnosis of an epithelioid mesothelioma metastasis. Calretinin, a helix–loop–helix structural domain found in calcium-binding proteins and widely expressed in neural tissue, is expressed in most cases of epithelioid mesothelioma [8]. For radiological investigations, ESMO (European Society For Medical Oncology) recommends using CT scanning of the thorax for the localization of tumor sites and distant metastases or detecting early response to treatment. They recommend also MRI in special situations where tumor delineation is necessary [9]. But the diagnosis of the secondary malignant mesothelioma in the oral cavity, as in the present case, is based on the presence of known history of the tumor. Even with the presence of the primary tumor, it is necessary to make a definite diagnosis of an assumed oral metastases to allow for an appropriate management. Although the clinical behaviour and the view of the primary oral squamous cell carcinoma (OSCC) is unlikely to be misdiagnosed for a metastatic lesion by an experienced surgeon, OSCC is the most likely diagnosis of a persistent mass, without obvious traumatic or infectious origin. Wide surgical excision is often an acceptable treatment for the management of OSCC, whereas in a metastatic mesothelioma case, it will be inappropriate [10]. The current effective standard treatment for mesothelioma is the addition of bevacizumab to pemetrexed plus cisplatin which significantly improves the overall survival [11]. Unfortunately, there was no effective standard treatment for mesothelioma during the follow-up period of the present patient. Therefore, another different regimen of chemotherapy was prescribed. Although the cisplatin plus pemetrexed therapy of the present patient was the standard of care in the first-line treatment, the prognosis was poor and the patient succumbed to the disease.

Malignant mesotheliomas frequently recurred locally in the chest and abdomen. Metastases occur at a relatively late stage of the disease. Kannerstein and Churg [12] reported metastases in 18/50 autopsy cases. Distant metastases are very rare, especially in the oral region. Primary breast carcinomas are the most common types of tumour to metastasize to the jaw bones while primary lung carcinomas are the most common types of tumour to metastasize to the oral soft tissue [13]. These oral metastases represent about 1 % of oral malignances, and there are more cases reported arising in the jaw bones than in the oral soft tissues with a ratio of approximately 2:1 [14]. The case presented in this report is only the first report of a mesothelioma metastatic to the retromolar trigone. Although Kruse et al. [13] and Hirshberg et al. [6] reported that metastases of mesothelioma, although rare, tend to involve the oral soft tissues, especially the tongue. Sinon et al.[3] reported that metastases to oral region are mostly seen in the tongue and the attached gingiva. One possible explanation for the tendency towards the tongue and the attached gingiva might be the rich capillary network, especially where chronically inflamed gingiva trap malignant cells and the fragmented basement membranes of proliferation capillaries allow easier penetration by malignant cells than in more mature blood cells [15].