Tumors of the minor salivary glands are an important area in oral surgery and pathology. A relatively high proportion of these are malignant, especially in the tongue, floor of the mouth and retromolar area. Although, as observed in major glands, pleomorphic adenoma (PA) and mucoepidermoid carcinoma (MeC) are the most common benign and malignant minor salivary gland tumors, respectively, some tumors such as canalicular adenoma, ductal papillomas, polymorphous low-grade adenocarcinoma and clear cell carcinoma NOS occur exclusively in minor salivary glands, while high-grade malignant tumors, for example salivary duct carcinoma and oncocytic carcinoma, are rare. Small parts of MeC arise in the jaws (central MeC), suggestive of odontogenic origin. Intraoral tumors are susceptible to trauma or inflammation-related ulceration. Histopathologically, benign minor salivary gland tumors have occasionally incomplete capsules and are juxtaposed against surrounding tissues. Furthermore, inflammation may cause various pseudomalignant changes of the tumors. As adenoid cystic carcinoma (AdCC) is common in minor salivary glands and shares architectural and cellular differentiating characteristics with PA, it is sometimes difficult to distinguish between these neoplasms in small biopsy specimens. Activity of cellular proliferation and immunolocalization of S100 protein may be helpful in the differential diagnosis. In AdCC, down-regulation of p27 protein caused by ubiquitin-mediated degradation by S-phase kinase-associated protein 2 (Skp2) overexpression is closely correlated with metastasis and low survival rate, indicating that reduced expression of p27 and overexpression of Skp2 could be good predictive markers of AdCC.
The clinical and pathological differentiation from tumor-like lesions including necrotizing sialometaplasia and adenomatous hyperplasia is also important.

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The histopathological diagnosis of salivary gland tumors is sometimes difficult, because the tumors have various histologic patterns and manifold tissue components coexist in a histologic pattern. Therefore, the differential imaging diagnosis of a benign and malignant tumor in the salivary gland is also sometimes difficult.
A salivary gland lesion in which the border is slightly unclear is sometimes a malignant tumor, even though the borderline looks almost clear on the images. Therefore, in the imaging diagnosis of salivary gland tumors, the clearness of the boundary on the images is very important and its cautious interpretation is essential; the clearness should be judged not by CT but by ultrasonography and MRI. Moreover, the CT and MRI images should be observed by optimal indication on a DICOM Viewer, if possible.
Regarding major salivary gland tumors: over 70% of parotid gland tumors are benign, 40% of submandibular gland tumors are malignant, and 80% of sublingual tumors are malignant. These figures are important when interpreting diagnostic images of major salivary gland tumors. A parotid gland tumor in which the border is not always clear should be suspected as malignant. A lesion that is confirmed as a sublingual gland tumor on diagnostic images should be diagnosed as a malignant tumor.
Concerning minor salivary gland tumors: when the tumor is small, a borderline is often clear even though the tumor is malignant. Hence, imaging findings of a lesion with a clear boundary are not evidence of a benign tumor in the minor salivary gland. In malignant salivary gland tumors of the palatal region, particular attention should be paid to weak bone invasion, which cannot be detected on imaging findings. In the lip and buccal region, ultrasonography is the most effective imaging modality. It is necessary to remember that mucoepidermoid carcinoma occurs also in the jawbones.

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Malignant salivary gland tumors are rare and their pathologic type is mostly adenocarcinoma, which is relatively slow-growing. Because the tumors are considered to be radioresistant, the first choice of treatment is surgery and conventional radiotherapy is usually combined when the tumor margin is close or incomplete. Recently, the availability of heavy ion beam therapy has increased the cure rate of radioresistant tumors. This article reviews the role of conventional radiotherapy, the prospects for heavy ion beam therapy, and emerging problems in the treatment of malignant salivary gland tumors.

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Surgical resection is the primary treatment of choice for both benign and malignant salivary gland tumors.
From 2001 to 2010, 181 patients with salivary gland tumors were treated: 63 tumors originated in the parotid gland, 23 in the submandibular gland, 5 in the sublingual gland and 90 in the minor salivary glands. Histologically, 115 tumors were benign and 66 tumors were malignant.
Preoperative diagnosis is one of the most important decision-making factors in the surgical treatment of salivary gland tumors, so diagnostic imaging modalities such as CT, MRI, US and PET were combined with FNAC or biopsy.
Surgical treatment of benign salivary gland tumors consisted of adequate local excision. A partial resection of the lobe with preservation of the facial nerve was performed in the benign tumors of the parotid gland, and a more limited “extracapsular dissection” (ECD) was indicated in selected cases. Benign tumors arising in the submandibular gland were excised through a simple excision of the gland itself. Benign tumors arising in the minor salivary glands were excised with a small cuff of margin. These surgical treatments resulted in no tumor recurrence. Meanwhile, treatment of malignant salivary gland tumors depended on the histologic grade of malignancy. Generally, surgery for tumors with low-grade malignancy consisted of a resection of the tumor with smaller clear margins without neck dissection, treatment of tumors with intermediate grade of malignancy consisted of the same clear margins as for squamous cell carcinomas with neck dissection, and treatment of high-grade malignant tumors required extended resection of the tumor with neck dissection, followed by radiotherapy or chemoradiotherapy. In 66 patients with malignant tumors, the disease-specific survival (DSS) rates at 5 and 10 years were 92.4% and 80.2%, respectively. The 5- and 10-year DDS rates were both 100% in 28 patients with low-grade malignant tumors, 100% and 83.3% in 23 patients with intermediate-grade malignant tumors, and 72.9% and 50.0% in 15 patients with high-grade malignant tumors, respectively.
The mainstay of treatment for all salivary gland tumors is surgery. The type and extent of surgery should be decided according to the histology of tumors, therefore, more precise preoperative evaluation of tumors including imaging diagnosis and FNAC is important. More aggressive adjuvant chemo- or chemoradiotherapy should be combined with extended surgery for high-grade malignant tumors.

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The purpose of this study was to investigate the detailed oral function and perception (warm, cold, tactile and thermal pain) of the oral mucosa of 10 postoperative mandibular cancer patients. The age of the patients ranged from 59 to 82 years. Oral function was evaluated using the low-adhesive color-developing chewing gum method, the Occlusal Prescale, the modified questionnaire of Yamamoto's masticatory grade, the Japanese monosyllable intelligibility test, and the whole mouth gustatory test. Perception was measured at two points on the lower lip and four points on the tip and dorsum of the tongue.
Yamamoto's masticatory grade (subjective evaluation) did not agree with masticatory performance (objective evaluation). Regarding Japanese monosyllable intelligibility, the patients had mild disorder. There were no differences in gustatory threshold between the patients and normal subjects. On the affected side, improvement of the heat and thermal pain thresholds was slower than that of the coldness and tactile thresholds.

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The syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH) is characterized by hyponatremia induced by a secretion disorder of an antidiuretic hormone and has been recognized in association with various conditions including malignant disease. On the other hand, hyponatremia during treatment of patients with cancer may be caused by SIADH, which is rarely caused by anticancer drugs. SIADH is not commonly associated with the field of oral and maxillofacial surgery and there are few case reports. We report a case of SIADH that developed during chemo-radiotherapy in a patient with oral cancer.
A 55-year-old woman with malignant tumor of the maxilla underwent chemo-radiotherapy. We performed systemic chemotherapy with S-1 at 100 mg/m² on days 1-21 and cisplatin (CDDP) at 81 mg/m² on day 11, in addition to radiotherapy followed by a radical dose of 68 Gy/34 fractions of external beam radiation. On day 17, she lapsed into a coma (Japan Coma Scale I-1), and her serum sodium concentration exhibited a sharp decrease to 98 mEq/L. Since the patient presented none of dehydration, a particular history of related disorders, serum hypoosmolality accompanied by urine hyperosmolality, or persistent urinary sodium excretion, we diagnosed that the hyponatremia was due to SIADH induced by the anticancer drug. After treatment with fluid restriction and sodium supplements, she regained consciousness and achieved an appropriate serum sodium level. We consider that a suitable early response is important when hyponatremia occurs, and that serum sodium should be measured frequently for SIADH during and after chemotherapy and chemo-radiotherapy with CDDP.

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