148 P27- Poster session: Tuesday, April 27, 1999 evaluation of tissue obtained from surgical treatment of cysts that had not been suspicious for malignant disease be- fore or during surgery. In two patients, the cyst was located in the anterior part of the mandible, a third patient had a cyst related to an impacted lower third molar, and the fourth patient showed a cyst in the anterior part of the maxilla related to an impacted canine. In one patient the cyst in the anterior part of the mandible had been treated by cystosto- my and been diagnosed as a keratocyst. During clinical and radiological follow up a second cystostomy 7 years after the first treatment had become necessary due to stagnation in reduction of size of the cystic formation. The tissue obtained in the second surgery showed an invasive squamous cell car- cinoma. In the other three cases a squamous cell carcinoma could be diagnosed after first surgery. Immediately after di- agnosis all four patients underwent radical tumor surgery, in two cases including resection of regional lymph nodes. All four patients are free of tumor recurrence with postoperative follow up ranging from two months to 11 years. Cfinical, radiological, histopathological and intraopera- tive images will be presented, underlining the extreme im- portance of histological evaluation of any tissue material ob- tained from surgical treatment of odontogenic cysts. 30. Effects of Chemotherapy on the Metastasis of Oral Squamous Cell Carcinoma in the Orthotopic Implantation Model Kawashiri, S., Kumagai, S., Kojima, If., Moriyama, M., Kakihara, K., Yamamoto, E. Department of Oral Surgery, School of Medicine, Kanazawa University, Japan The presence of metastasis is the most important factor in the prognosis for patients with oral cancer, and success with cancer therapy depends on whether metastases can be con- trolled. The effects of chemotherapy on the metastasis of oral squamous cell carcinoma (SCC) were evaluated in a nude mouse model of the metastasis induced by orthotopic implantation of the OSC-19 cell line, a highly invasive and metastatic human oral SCC. In the first experiment, OSC- 19 cells were implanted into the oral floor of the mice. In mice exhibiting metastatic changes, cisplatin (CDDP) or pe- plomycin sulfate (PEP) was intraperitoneally administered 7 or 14 days after implantation. The chemotherapeutic effects of the two drugs and of the two times of administration were compared. In the control group, the cervical lymph node metastasis rate was 90.9%, but in the chemotherapy group treated 7 days after implantation, it was 45.5% (P<0.05). In the second experiment, OSC-19 cells were implanted into the tongue. Subsequently, tumor resection was performed alone (Group S alone) or in combination with preoperative chemo- therapy (Group C+S). The cervical lymph node metastasis rate for the two groups was compared. The lymph node metastasis rate was 81.8% for Group S alone but 18.1% for Group C+S. Thus metastasis to the cervical lymph nodes was markedly inhibited by the combination of tumor resec- tion and preoperative chemotherapy (P01). The results showed that chemotherapy at an early stage was more effec- tive for inhibiting lymph node metastasis of oral SCC. 31. Immunohistochemical Analysis of the p53 Tumor Suppressor Gene Product in Oral Leukoplakia Kikegawa, A., Sakai, E., Shimamoto, H., Hirano, Y., Enomoto, S. The Second Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo, Japan Squamous Cell Carcinoma (SCC) is the most frequent ma- lignancy in the oral cavity. P53 protein has been reported to be expressed at high levels in malignant lesions, while the levels in premalignant lesions has yet to be addressed. In this study, the oral leukoplakia with epithelial dysplasia were examined. Forty one incision or excision samples diagnosed as leuko- plakia with epithelial dysplasia in the oral cavity were ob- tained. All samples (formalin-fixed, paraffin embedded) were examined immunohistochemically for overexpressionof p53 protein with monoclonal antibody BP53 12. As the result, 1) Twenty two out of 41 leukoplakia cases were positive for p53 protein. 2) p53 protein is overexpressed in premalignan t lesions, especially in the cases with moderate and severe epithelial dysplasia. 3) Malignant transformation during clinical observation was seen in 11-cases. Ten out of 11 cases were positive for p53 even before malignant transformation. Since in cancerization cases, p53 staifiing was detected even before malignant transformation of oral leukoplakia to squam- ous cell carcinoma, it is indicated that p53 accumulation occurred at a early stage of cancerization. In conclusion, the immunohistochemical analysis of p53 pro- tein is suggested to be a useful diagnostic procedure for oral leukoplakia which may develop into oral SCC. 32. Unilateral Mandibular Widening by Intraoral Distracion Osteogenesis Lopez, R, Guerrero, C., Bell, W., Rojas, A., Meza, L., Pantin, C. Caracas, Venezuela Introduction Individuals with mandibular arch asymmetry, unilateral Bro- dy syndrome (Scissors bite), Class II subdivision malocclu- sions, as well as asymmetric transverse mandibular de- ficiency with anterior teeth crowding represent a difficult clinical situation to treat. Unilateral mandibular widening by means of intraoral distraction osteogenesis was designed