An analysis of patients with salivary gland cancers shows that risk factors for positive surgical margins include age, tumor stage, and treatment center.

“Salivary gland cancers are rare malignancies in the oropharynx that are primarily treated with surgery because they are relatively resistant to other therapies, such as radiation, chemotherapy, and immunotherapy,” Craig Bollig, MD, explains. “Surgical margins have been associated with cancer recurrence rates and survival in previous studies. However, because these tumors are so rare, there was not much information on risk factors for positive margins in this population prior to this study. Additionally, one of my primary clinical interests is transoral robotic surgery (TORS), which involves using a surgical robot to remove tumors located deep in the throat in a minimally invasive fashion through a patient’s mouth.”

According to Dr. Bollig, previous research on the use of TORS in this population was limited, as were data on whether it was associated with similar positive margin rates compared with traditional surgical approaches.

For a study published in American Journal of Otolaryngology—Head and Neck Medicine and Surgery, Dr. Bollig and colleagues obtained data from the National Cancer Database on patients with oropharyngeal salivary gland malignancies (OPSGM) from clinical T stages 1 to 4a who underwent surgical resection between 2010 and 2017. The researchers analyzed risk factors for positive surgical margins (PSM) using logistic regression and overall survival (OS) using Kaplan-Meier and Cox proportional hazards models.

“Our objectives were to determine the clinical factors associated with positive margins, including TORS,” Dr. Bollig notes. “We also wanted to investigate the impact of giving radiation therapy after surgery in patients with positive margins to see if that improved survival. Because these are rare tumors, we used a large national database for this project.”

Risk Factors for Positive Margins & Associations With Survival

The analysis included 785 patients, nearly a quarter of whom—21%—had PSM. Individuals with PSM were slightly older than those without PSM (mean age, 61.2 vs 57.3). The most common tumor subsites were the base of the tongue for those with PSM (44.2%) and the soft palate for individuals without PSM (50.3%).

The study “is the largest review evaluating risk factors for positive margins in this patient population,” according to Dr. Bollig.

“We found that older age, receiving treatment at lower volume institutions, stage 4 tumors, and adenoid cystic carcinomas were all associated with positive margins, independent of other clinical factors (Table),” he continues. “TORS was associated with a similar rate of positive margins compared with more invasive, traditional surgical approaches. We also found that giving radiation therapy after surgery in patients with high grade tumors was associated with improved survival.”

Positive margins were associated with poorer OS, which aligns with prior research, according to the study results. Factors independently associated with OS on multivariable analyses included positive margins (ref. negative; HR, 1.63; 95% CI, 1.03-2.59), age (HR, 1.06; 95% CI, 1.04-1.08), high grade tumor (ref. low; HR, 3.20; 95% CI, 1.71-6.00); T4 stage (ref. T1; HR, 2.53; 95% CI, 1.29-4.96), and node-positive (c1-c3) stage (ref. N0; HR, 2.24; 95% CI, 1.33-3.76).

Implications for Counseling Patients Prior to Surgery

“We can use this information to identify higher risk patients prior to surgery and counsel them appropriately,” Dr. Bollig says. “This study also provides some evidence that TORS is associated with similar rates of positive margins compared with traditional, more invasive surgical approaches.” 

The similar rates observed with TORS is important, as use of the technology has increased in the last decade, according to the study results. Future research is needed regarding recurrence rates and the impact of radiation therapy, Dr. Bollig notes.

“The National Cancer Database provides information on large numbers of patients to allow us to perform research on rare tumors that we cannot easily do from single institutions,” he says. “However, while it has survival information, it, unfortunately, does not have information on cancer recurrence rates. We commonly recommend giving additional radiation therapy after surgery for patients with positive margins. In this study, however, we only saw a survival benefit for additional radiation therapy in patients with high grade tumors. We need more information on the effect of radiation therapy in patients with low grade tumors in the oropharynx with positive margins. It may decrease recurrence rates, but not impact survival.”