We studied 5231 patients with odontogenic tumor who visited and were treated at the 61 institutions certified as training facilities by the Japan Society for Oral Tumors, which comprise 25 dental university hospitals, 28 medical university hospitals, and 8 general hospitals (1995-2004) . These tumors were reclassified according to the new WHO classification revised in 2005 and the clinicopathological data were analyzed. The patients were 2582 (49.4%) males and 2649 (50.6% ) females (male : female ratio, 1 : 1.03) .
Histologically, the tumors contained 1460 ameloblastomas, 1258 keratocystic odontogenic tumors and 1079 odontomas. These tumors constituted 74% of all the cases.

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Many kinds of guidelines and general rules for clinical studies on the treatment of cancer have been reported. The histopathological judgment of chemo-radiotherapeutic effects is based on the Oboshi-Shimosato grading, which is divided into 5 classes (Grade 0 to IV) according to the damage of cancer cells or nests.
Generally, the area of destroyed cancer tissue is measured as a reference point for biopsy. This method is still being used today and there are no rules for the scope of observation. Moreover, it is not easy to correctly judge whether a cell is alive or dead and there are different judgments by pathologists. In other words, the histopathological judgment is ideologic and true scientific evidence is lacking.
I have examined many problems involved in judging the post chemotherapeutic state of surgical material by microscopic obersvations.
At present, it is important for histopathological judgment to do the following:
(1) We must make glass slides of surgical materials and observe all of them (for using the BLSS method) if possible.
(2) For the judgment, photographs of the damage of the cells, nests and stroma are used.
(3) The superficial change of the epithelium is valid for judgment, similar to damage to the deeper cancer tissue.
To reach a solution, it is necessary to discuss the difference of invasive front in terms of prognosis and predictive factors.

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From January 2000 to December 2005, 56 oral cancer patients were treated with preoperative radiotherapy at Hokkaido University Hospital. All loco-regional recurrences appeared in the radiation field. Good local control rate was seen in patients treated with concomitant intra-arterial or intra-venous chemotherapy, compared with radiotherapy alone.
Local recurrence rate was worse in cases where the interval from the end of irradiation to the date of operation was longer than 3 weeks.

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We report a series of 136 patients with advanced oral cancer who received preoperative concurrent chemoradiotherapy (CCRT) followed by surgery and who were studied clinically and histopathologically, and the indication of minimally invasive surgery was evaluated. The results and conclusions were as follows: 1. The CR (complete response) of the primary tumor was 60.3% and the overall response rate was 92.7%. Histological effects were Grade II b and above, i.e. effective, in 84.6% and Grade III, N, i.e. pathological CR, in 73 of 82 (89.0%) in CR cases. The CCRT was also very effective histologically, and a correlation was observed between clinical effects and histological effects. 2. The residual tumor grade (R Grade) in the resected specimen is considered to be useful as a prognostic factor. 3. Histological effects were satisfactory in good PR and CR cases on CCRT. In such cases, minimally invasive surgery is considered to be applicable even in advanced cases, and improvements in the postoperative QOL can be expected by preservation of the oral organs and functions.

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Histological change of advanced oral cancers following concurrent chemoradiotherapy was examined with semiserial whole surgical specimens. Subjects included six tongue squamous cell carcinomas (SCCs), two oral floor SCCs and three lower gingival SCCs, and all the tumors were preoperatively treated by the combination of radiotherapy and superselective intraarterial infusion of CBDCA or oral administration of TS-1^®. Clinical effect was assessed as CR in three cases, PR in five, MR in two and NC in two.
The distribution of residual cancer nests was categorized as the superficially-located and deeply-located patterns. It was noteworthy that the pattern of residual cancer nests and the histological effect were different between sections even in the same tumors. Furthermore, a few viable cancer nests were observed exclusively in the advancing edge in tumors assessed as Grade 2b (Oboshi-Shimosata classification), where most of the cancer nests were degenerative or necrotic. This finding suggests that the extent of resection could not be reduced even in tumors that responded well to preoperative therapy.
In the present cases, the histological effect of chemoradiotherapy was evaluated as Grade 4a in two cases, Grade 2b in four, Grade 2a in five and Grade 1 in one. Tumors of the PR showed a wide variation of histological evaluation from Grade 1 to Grade 4a, resulting in a discrepancy between the clinical and histological evaluations.

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There have been few studies on the spread pattern of carcinomas of the floor of the mouth even though this is crucial for navigation during ablation surgery for those tumors. In this preliminary study, anatomical structures constituting the floor of the mouth in resected materials from 20 patients with carcinoma of the floor of the mouth were histopathologically analyzed in terms of extent of invasive tumor cells. In 17 of the 20 patients, tumor cells extended into deep tissues. Sublingual gland and intrinsic tongue muscle were the most affected anatomical structures, being observed in 13/17 patients (77%) and 12/17 patients (71%), respectively. Tumor cells extending into the mylohyoid muscle or submandibular gland were not observed in this series. According to the sub-sites where tumors arose, there was a trend toward enhanced rate of tumor cells extending into the intrinsic tongue muscle and genioglossus muscle in the median type compared with the lateral type.
Conclusive results could not be drawn from this preliminary study. Further detailed investigation based on clinico-pathological observation of many cases is required to obtain more information for oral surgeons.

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We report a case of upper gingival primary peripheral ameloblastoma occupying the masticatory space, centering on the infratemporal fossa.
A 72-year-old male had noticed a painless mass of the left upper gingiva 6 months earlier. Upon oral examination, the tumor extended to the buccal mucosa and the soft palate, focused around the gingiva at the left maxillary. CT and MRI findings revealed that the tumor was in contact with the posterior wall of the maxillary sinus and surrounded the whole circumference of the coronoid process. Consequently, the tumor extended across the zygomatic arch on the upper side, to the pterygomandibular space interiorly, and to the anterior border of the masseter muscle laterally. The lesion was diagnosed to be a peripheral ameloblastoma on biopsy. The tumor was resected by a combination of hemicoronal incision and transbuccal approach.
The surgical technique ensured a good surgical field for the masticatory space centering on the infratemporal fossa and allowed secure removal of the primary tumor. In addition, postoperative aesthetic and functional damage were slight and led to satisfactory results.

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We report a case of pleomorphic adenoma in the accessory parotid gland. In March 2004, a male in his late twenties visited our hospital with the chief complaint of a mass in the right cheek. MRI, ultrasonic, and sialography showed that the mass was located in the right accessory parotid gland.
Specimens obtained by needle biopsy suggested that the mass was mostly pleomorphic adenoma. We removed the mass that was located anterior to the parotid gland and surrounded by masseter muscle, zygomatic branches of facial nerves, and parotid duct, with a parotidectomy-style excision.
The mass was removed easily without postoperative complications such as facial paralysis. The final pathological diagnosis was pleomorphic adenoma.

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Metastasis to the lateral retropharyngeal lymph node, which is the Rouviere node (RN), is frequently observed in naso and hypopharyngeal carcinomas but rarely in oral carcinoma. We report a case of metastasis to RN from upper gingival carcinoma detected by headache.
A 76-year-old male visited us with the complaint of contact pain of the right upper gingiva. A biopsy was performed, and the lesions were diagnosed as squamous cell carcinoma. On CT examination there was no metastasis to the cervical lymph node and other regions, so a partial maxillectomy following neoadjuvant chemotherapy was performed. Nine months after the operation, the patient complained of a headache. RN metastasis on the right side was detected by CT scan, and radiotherapy was performed to RN and the neck area. The tumor reduced temporarily and the headache disappeared, but he died 9 months after metastasis was first discovered.

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