Adjuvant radiotherapy in pT3-4N0M0 major salivary gland Cancer without other adverse features.

OBJECTIVE

To investigate adjuvant radiotherapy (aRT) utilization and associated differences in overall survival (OS) in pT3-4N0M0 major salivary gland cancer (MSGC) without evidence of other adverse pathologic features.

METHODS

The 2006 to 2018 National Cancer Database was queried for patients with MSGC classified as pT3-4N0M0. Patients with evidence of lymphovascular invasion or positive surgical margins were excluded. Multivariable binary logistic and Cox regression models adjusting for patient demographics, pathologic features including histology, and treatment were implemented.

RESULTS

Of 897 patients satisfying inclusion criteria, 368 (41.0 %) underwent aRT. Compared with those not undergoing aRT, patients undergoing aRT were younger (median [IQR] 61 [49-72] vs. 67 [53-78] years) and more frequently had adenoid cystic carcinoma (AdCC) (18.2 % vs. 10.4 %) and high-grade disease (33.7 % vs. 21.6 %) (P < 0.001). On multivariable binary logistic regression, age at diagnosis (aOR 0.98, 95 % CI 0.97-0.99) and Black race (aOR 0.50, 95 % CI 0.32-0.77) were associated with decreased odds of undergoing aRT (P < 0.005); AdCC (aOR 2.58, 95 % CI 1.54-4.32), high grade (aOR 1.81, 95 % CI 1.04-1.98), pT4 classification (aOR 1.43, 95 % CI 1.04-1.98), and neck dissection (aOR 1.41, 95 % CI 1.05-1.90) were associated with increased odds (P < 0.05). Patients undergoing aRT had higher 5-year OS than those not undergoing aRT on Kaplan-Meier (82.9 % vs. 67.0 %, P < 0.001) and multivariable Cox (aHR 0.50, 95 % CI 0.37-0.66, P < 0.001) analyses.

CONCLUSION

aRT was utilized in approximately 40 % of patients with pT3-4N0M0 MSGC without evidence of other adverse pathologic features. aRT was associated with higher OS, highlighting the continued need for efforts promoting guideline-recommended care.

LEVEL OF EVIDENCE: 4 LAY SUMMARY: pT3-4N0M0 major salivary gland cancer without evidence of other adverse pathologic features represents a rare, moderate-risk disease category with high variation in treatment strategies depending on histopathology and physician and patient preferences. Our study of this disease category suggests that adjuvant radiotherapy is associated with higher 5-year overall survival.