4887 - Impact of tumor site and adjuvant radiotherapy on survival of adenoid cystic carcinoma: a SEER database analysis

Background

Adenoid cystic carcinoma (ACC) is a rare salivary gland tumor, comprising less than 1% of head and neck neoplasms. Adjuvant radiotherapy (aRT) is suggested for late-stage disease (stage III or IV); however, recent evidence suggests that it may be associated with improved survival even for early-stage disease. Moreover, the prognostic significance of tumor location on overall (OS) and ACC-specific (ACC-S) survival is unclear. We sought to address these knowledge gaps via analyses of the Surveillance, Epidemiology and End Results (SEER) database.

Methods

Intraoral minor (m) and major (M) ACCs from the SEER database (1973-2015) were selected for analysis. Information on age, sex, race, site, stage, treatment and survival was retrieved. The associations of tumor site and aRT with OS and ACC-S were estimated using hazard ratios (HR) and corresponding 95% confidence intervals (CI) obtained via Cox regression models adjusted for covariates as appropriate. Analyses were done using Stata 15.1 (StataCorp LP, College Station, TX).

Results

There were 635 minor and 1,064 major (parotid: n = 547, submandibular: n = 470, sublingual: n = 47) ACC cases included in the analyses. Late-stage patients (49% of total) were significantly more likely to have received aRT (76% vs. 66%; P < 0.01) compared to those with early-stage disease. Submandibular was the only tumour site that demonstrated statistically significant survival differences compared to the other sites; i.e., worse OS (HR = 1.4; 95% CI = 1.1-1.8) and ACC-S (HR = 1.7; 95% CI = 1.2-2.3) compared to minor ACCs. This difference was only evident for late-stage tumours: stage IV submandibular cases had worse OS (HR = 2.1; 95% CI = 1.5-2.8) and ACC-S (HR = 2.4; 95% CI = 1.7-3.4) compared to stage IV minor ACCs. Overall, aRT was associated with better OS (HR = 0.7; 95% CI = 0.6-0.9) and ACC-S (HR = 0.8; 95% CI = 0.6-1.1). This beneficial effect was more pronounced and statistically confirmed only in stage IV disease.

Conclusions

These results, based on SEER data, suggest that aRT is associated with favorable survival only in late-stage ACC and that, among these late-stage tumors, submandibular gland ACCs have substantially worse prognosis than other sites, irrespective of aRT.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Academy of Athens PhD Scholarship to Jason Tasoulas; UNC Lineberger Tier 3 Developmental Award funds and the University Cancer Research Fund to A.L. Amelio.

Disclosure

All authors have declared no conflicts of interest.