MGSCC is relatively rare, and few reports have analysed the treatment strategies and prognostic factors in a significant number of cases.[10] In addition, since palatal cancer involving the hard palate and MGSCC show similar clinical findings, some reports have analysed the combination, but few reports have analysed only MGSCC.[11–16] This study analysed the management methods and prognostic factors of MGSCC in 90 cases. Eskander at al. reported that poor differentiation in tumours was an independent predictor of disease-specific survival rate.[14] Poeschl et al. reported that T staging and grading do not have a significant impact on long-term survival of patients.[6] Yang et al. reported statistically significant associations among patient survival rate and tumour differentiation grade, T staging, cervical lymph node metastasis, and local recurrence.[15] Ojima et al. reported that the posterior region cancers showed poor prognoses compared with the anterior and molar region cancers.[8] In the multivariate analysis, site of occurrence contributed significantly to the survival rate in our study. Posterior region MGSCCs showed significantly poor prognoses compared with the anterior and molar region types. Nine of 20 cases with poor prognoses showed locoregional recurrence after the primary surgery, while 5 of the 9 cases were posterior region cancers. It is suggested that posterior region cancers show poor prognoses due to the difficulties encountered in including sufficient safe areas in resection, in spite of the surgical margins determined as negative.
Prophylactic neck dissection is recommended in cases of cervical lymph node metastasis with MGSCC.[17–21] In our study, 8 patients in the N0 stage underwent prophylactic neck dissection, and 64 patients were closely monitored without any treatment. One patient treated with prophylactic neck dissection developed cervical lymph node metastasis. In recent years, several reports have recommended prophylactic neck dissection even in early stages.[1, 20, 22] Moratin et al. suggested the concept of prophylactic neck dissection in early tumours with clinically negative neck status.[22] Poeschl et al. reported that prophylactic neck dissection did not significantly improve overall survival rates and did not prevent the rate of regional recurrence in cN0-staged patients with MGSCC and palatal SCC.[6] In our study, 11 of the 47 cases in T1 and T2 stages (23%) developed postoperative cervical lymph node metastases, which were treated by neck dissection. The 5-year overall survival rate in these patients was 80%, indicating that neck dissection even after subsequent cervical metastasis is very effective. Therefore, we suggest that N0-staged MGSCC patients should be closely monitored, and neck dissection should be performed immediately upon the onset of cervical lymph node metastasis.
The overall survival rates of patients with MGSCC have been previously reported as 24–71%.[6, 15, 20, 23] Binahmed et al. reported the 5-year overall survival rate as 33%.[13] Yang et al reported the 5-year overall survival rate as 57.5%.[15] A critical comparison could not performed because their analysis included carcinomas of the hard palate. Morice et al. reported the 5-year overall survival rate as 32% for MGSCC. In their analysis of 47 patients, 12 cases were in the T1 to T3 stages (26%), and 35 were in the T4 stage (74%). In contrast, our study revealed the 5-year overall survival rate as 82.1%. In our study, 60 cases were in the T1 to T3 stage (66.7%), while 30 cases were in the T4 stage (33.3%). Hence, the lower survival rate in the study by Morice et al. could be attributed to the greater number of advanced cases. However, even the 5-year disease-specific survival rate (76.7%) of cases in advanced T4a stage in this study was better than that of corresponding cases (54%) in their study. The better survival rate in our study could be a result not only of the smaller number of advanced cases but also of better results for the advanced cases. Morice et al. and Yang et al. treated most patients surgically. However, we performed combination therapy including surgery and chemoradiotherapy for advanced cases. This could be the reason for better survival rates even in the advanced cases of our study.
Twenty patients died during the study period, including 3 deaths due to other diseases and 17 due to MGSCC (T1: 2 cases, T2: 6 cases, T3: 3 cases, T4a: 6 cases, and T4b: 3 cases). Seven patients died in primary recurrence, 2 patients in cervical recurrence, one in primary recurrence with lateral retropharyngeal (Rouviere) lymph node metastasis, one in primary and cervical recurrences, and 6 patients died in distant metastases including 2 patients with untreatable primary and cervical recurrence with Rouviere lymph node metastasis. Of the 17 deaths due to the MGSCC, 6 deaths (35.3%) occurred due to distant metastases, suggesting that management of distant metastasis is particularly important for improving future treatment outcomes.