SDC exhibits an aggressive clinical behavior and especially poor prognosis that is characterized by multiple nodal metastases, early DM, and a high rate of local recurrence [
3,
4]. According to reports in the literature [
3], the rates of nodal metastasis, DM, and local recurrence are approximately 60, 50, and 50%, respectively [
3]. Moreover, the mean overall survival was 56 months and the 5-year disease-free survival rates for stage I–IV SDC were approximately 42, 40, 30, and 23%, respectively [
3].
Recently, prognostic factors for SDC have been extensively studied in large numbers of patients and several factors, including tumor size, anatomical location, age, positive infiltrative margin, PNI, regional recurrence, nodal metastasis, and DM have been suggested to be associated with a poor prognosis [
3,
4,
9,
10]. In particular, it has been suggested that a large tumor size of >3 cm is associated with a poor prognosis [
11], while a small tumor size of <2 cm is associated with a more favorable prognosis [
9]. However, the prognostic data described above were established based on the findings of SDC of major salivary gland origin, owing to the fact that the majority of SDC cases arise in the major salivary glands, particularly the parotid glands. Therefore, prognostic data concerning SDC of minor salivary gland origin remains limited, because the incidence of SDC of minor salivary gland origin is extremely low compared to that of SDC of major salivary gland origin. A relatively favorable prognosis in patients with SDC of minor salivary gland origin compared to SDC of parotid gland origin was suggested based on the finding that the former was associated with less frequent regional LNMs in a review of the literature [
10,
12]. However, this less aggressive behavioral tendency of SDC of minor salivary gland origin is most likely due to the relatively smaller tumor size, because SDCs of minor salivary gland origin are detected earlier than SDCs of major salivary gland origin [
10]. There have been no reports describing the difference in prognosis between patients with SDC of minor salivary gland origin and patients with SDC of major salivary gland origin after matching for stage. Histologically, SDC resembles high-grade ductal carcinoma of the breast with a solid or cribriform growth pattern. The majority of immunohistochemical staining investigations [
1‐
3] have revealed similarities between SDC and breast carcinoma with positive immunostaining for epithelial markers such as cytokeratin and epithelial membrane antigen and particularly intense immunoreactivity for gross cystic disease fluid protein-15 (GCDFP-15), androgen receptor, and HER2/neu. It has been suggested that overexpression of HER2/neu and tumor protein p53 are associated with a poor clinical course, including early regional recurrences, DM, and low survival rates [
3]. Although no consistent therapeutic concept exists for this entity, complete surgical resection with radical neck dissection, followed by radiotherapy, has been suggested as the treatment recommendation for resectable SDC [
13,
14]. Postoperative radiotherapy has been suggested to improve locoregional control in a patient with advanced stage SDC [
13]. In particular, observations of PNI during a final pathological examination may lead to consideration of postoperative radiotherapy [
13]. Moreover, only limited data are available regarding the efficacy of chemotherapeutic agents. Therefore, no consensus exists for the efficacy of chemotherapy. Molecularly targeted therapy against HER2 protein with anti-HER2 monoclonal antibodies has been suggested to be contributive as a therapeutic target for patients with HER2/neu-positive SDC [
15,
16]. Anti-androgen therapy has also been evaluated in patients with androgen receptor positive SDC [
17].
In the present case, multiple regional LNMs and an elevated Ki-67 proliferation index were observed. Lymphovascular invasion and PNI were also apparent on histological examination. Therefore, multimodal therapy with induction chemotherapy, radical surgery, and postoperative adjuvant chemoradiotherapy was conducted. In fact, in the present case, induction chemotherapy with cisplatin led to a 24.0% reduction in tumor size, suggesting that chemotherapy is at least partially effective in treating patients with SDC. To the best of our knowledge, this is the first report describing the efficacy of multimodal therapy for SDC of minor salivary gland origin.
Additional studies are required to elucidate further the clinical outcomes of patients with SDC of minor salivary gland origin. Particular attention should be paid to the potential application of multimodal adjuvant therapy, especially when endeavoring to accumulate adequate experience of this rare type of tumor. Taking into account the aggressive clinical behavior of SDC, such as the high locoregional recurrence rate and early DM, multimodal therapy should be considered for the management of this high-grade malignancy.