Carcinomas of the mandibular gingiva are more common than those of the maxillary gingiva [5]. Mandibular gingival carcinoma invades the mandible in an early stage [6]. If it invades the mandible deeply, it cannot be expected to be cured by RT alone because radiation osteoradionecrosis occurs after high-dose RT [7]. In addition, the transfer of antitumor drugs to bone is poor and surgical resection is performed for carcinomas of the mandibular gingiva [3].
In stage III or IV, locally advanced SCC of the head and neck is usually treated by surgery or concurrent chemoradiotherapy [8–10]. The 5-year overall survival (OS) rate after resection for mandibular gingival carcinoma has been reported to be 38-80.6% [3, 4]. On the other hand, the 5-year disease-free survival rate of patients with cervical metastasis is about 25% [1]. In the present case, good control was achieved without resection. The combination of RT and S-1 might have been good. S-1 is an oral anticancer drug containing gimeracil and oteracil potassium in tegafur that is a prodrug of 5-FU. Gimeracil inhibits dihydropyrimidine dehydorogenase, which is a 5-FU-degrading enzyme, and oteracil potassium has the effect of suppressing gastrointestinal toxicity caused by 5-FU [11]. Gimeracil was reported to exert radiosensitizing effects on oral squamous cell carcinoma cells in vitro and in vivo [12]. Response rates of 46.2% and 28.3% were reported for early and late phase II clinical trials for advanced and recurrent head and neck cancer, respectively [13]. There are also some reports of CR with administration of a single agent for head and neck cancer and oral cancer [14]. In addition, elderly patients are considered to be tolerant for S-1 [15].
A severe acute complication occurred in our patient. It is desirable to reduce the side effects of chemotherapy as much as possible. Alternate day administration of S-1 may help to reduce side effects. This takes advantage of the fact that the cell cycle in humans is about one day, whereas that of cancer cells is 5–7 days [16–18]. In animal experiments, it was shown that the effects were the same and that side effects were reduced compared to alternate day administration and daily administration [17].
Patients with head and neck cancer who receive cumulative radiation doses of more than 50 Gy are more likely to have oral side effects and they have a higher risk of unplanned breaks in radiation therapy [19]. Our patient was hospitalized for one week due to loss of appetite and an oral side effect, but the low radiation dose of 30 Gy with S1 might have been an effective treatment option.
The abscopal effect is probably associated with our local control for lymph node metastases in the right neck region out of the radiation field. This effect is known that radiation shrinks tumors outside the irradiation field [20]. The biological mechanism underlying this effect remains unclear. To the best of our knowledge, there has been no study on an abscopal effect of mandibular gingival carcinoma. In our case, it is difficult to distinguish between the effects of chemotherapy and the potential for abscopal effects. There are some reports that CR was obtained only with S-1 [14] .In the present case, the combined use of S-1 is only for one week, and the effect of S-1 alone is considered to be limited. In addition, we could not confirm pathological diagnosis for lymph node metastases. It is possible that it was misdiagnosis for nodal clinical staging.
Because this study is a case study, it is difficult to define the indication for palliative chemoradiotherapy in an elderly patient with advanced SCC in mandibular gingiva. However, it is possible that some patients advanced SCC in mandibular gingiva were treated only by surgery, chemotherapy or radiation therapy although they were potential candidates of palliative chemoradiotherapy. Palliative chemoradiotherapy for advanced SCC in mandibular gingiva is therefore considered to be a therapeutic option.