Abstract
Purpose
To identify patient and tumor characteristics predictive of primary parotid malignancy.
Materials and methods
Records were reviewed for patients who underwent parotidectomy at the University of Wisconsin from 1994 to 2013. Patients with primary parotid neoplasms were separated into benign or malignant subgroups. A multivariate logistic regression model was employed to compare categorical (gender, lesion side, nature of presentation, recurrence) and numerical variables (age, tumor size) between the benign and malignant groups. Mean BMI was compared between the groups by univariate analysis.
Results
771 patients underwent parotidectomy from 1994 to 2013, and 474 had a primary parotid neoplasm. No relationship existed between malignancy and gender (p = 0.610), lesion side (p = 0.110), or BMI (p = 0.196). Mean age (p = 0.015) and tumor size (p = 0.011) were significantly different between the benign and malignant groups. Patient presentation was classified into three categories: symptomatic (n = 109), palpable and asymptomatic (n = 303), and incidentally noted on imaging (n = 57). From all patients with symptomatic, asymptomatic or incidentally noted masses, 41.3%, 10.6% and 5.3%, respectively, were diagnosed with malignant disease. There was a significant relationship between the patient’s initial presentation and malignancy (p < 0.001), and patients with facial nerve dysfunction or skin involvement had the greatest likelihood of malignancy. Finally, there was a significant association between malignancy and recurrence (p = 0.001).
Conclusions
In this study, age, tumor size, and nature of presentation were all associated with primary parotid malignancy. Understanding the impact of these features on the probability of malignancy is valuable in decision making and counseling of patients presenting with a newly diagnosed parotid neoplasm.
1
Introduction
Primary salivary gland neoplasms represent a diverse set of benign and malignant pathologies, accounting for 2%–5% of all tumors arising in the head and neck . Several large clinical reports examine salivary gland neoplasms and outline the most common benign and malignant subtypes . These studies are commonly more descriptive than quantitative, defining epidemiologic characteristics of different histological subtypes across all salivary glands. However, neoplasms arising in different salivary glands have unique clinical presentations, and as an Otolaryngologist it is important to understand the pathology, epidemiology, clinical features and risk factors related to malignancy at each salivary site.
The parotid gland represents the site where approximately 70%–85% of all salivary tumors arise . Importantly, the majority of primary parotid neoplasms are benign. Although the parotid gland has a lower benign to malignant ratio compared to other salivary glands, it accounts for 50% of all salivary malignancies . In this manner, the parotid gland represents an important site for the development of salivary gland cancers.
Literature focusing on parotid disease places emphasis on defining different surgical techniques , post-operative complications , and the utility of fine needle aspiration (FNA) in the management of patients with parotid tumors . Additional studies identify factors related to overall survival , occult neck metastases , and distant metastases in patients with parotid malignancies. Significantly, there is little information in the literature focusing on the identification of patient or tumor characteristics that could allow a more accurate clinical prediction of the probability of primary parotid malignancy.
Therefore, we carried out this study in order to identify patient and tumor characteristics predicting the probability of parotid malignancy in patients presenting with a newly diagnosed parotid mass. We performed a retrospective chart review of all patients (n = 771) who underwent parotidectomy at the University of Wisconsin (UW) between 1994 and 2013 to identify those with primary parotid neoplasms. Patient and tumor characteristics including age, gender, body mass index (BMI), lesion side, nature of presentation, tumor size and recurrence were examined to evaluate the relationship of these variables to the diagnosis of parotid malignancy.
2
Materials and methods
2.1
Review of electronic medical records and patient selection
After obtaining approval from the UW-Madison Health Sciences Institutional Review Board, the medical records of all patients who underwent parotidectomy at UW from 1994 to 2013 were reviewed. Records were evaluated to extract the following information: gender, age, nature of presentation, surgical pathology, tumor size (from surgical pathology and imaging), lesion side, body mass index (BMI) and recurrence after initial procedure. We included all patients with primary parotid gland neoplasms while patients who underwent parotidectomy for metastatic tumors, inflammatory conditions or other reasons were excluded. To evaluate characteristics predictive of primary parotid malignancy, patients with primary parotid neoplasms were divided into benign and malignant subgroups.
2.2
Statistical analysis
Statistical analyses were performed with the goal of identifying patient or tumor characteristics that were associated with the diagnosis of primary parotid gland malignancy. Nature of initial patient presentation was classified into three groups: symptomatic (discomfort, facial nerve dysfunction, recurrent infection, etc.), palpable mass and asymptomatic, or incidentally noted parotid mass on imaging. A multivariate logistic regression analysis was used to compare the following variables between the benign and malignant groups: gender, lesion side, nature of presentation, and recurrence were included as categorical variables while age and tumor size were evaluated as continuous variables. More than 20% of patients did not have an available BMI, so this factor could not be included in the multivariate analysis. The multivariate analysis was performed using the procedure PROC LOGISTIC from SAS/STAT software (version 9.3), and an odds ratio with 95% confidence interval (CI) was calculated for each variable.
A two-sample t-test with equal standard deviations (univariate analysis) was carried out using Graphpad Prism v6.0d to compare mean BMI between the benign and malignant groups. This univariate analysis was also employed to compare mean tumor size between malignant tumors that did or did not recur (as well as mean tumor size for benign tumors that did or did not recur). Means and 95% confidence intervals were calculated for each variable included in these univariate analyses. For all statistical work, a p-value less than 0.05 was considered statistically significant.
2
Materials and methods
2.1
Review of electronic medical records and patient selection
After obtaining approval from the UW-Madison Health Sciences Institutional Review Board, the medical records of all patients who underwent parotidectomy at UW from 1994 to 2013 were reviewed. Records were evaluated to extract the following information: gender, age, nature of presentation, surgical pathology, tumor size (from surgical pathology and imaging), lesion side, body mass index (BMI) and recurrence after initial procedure. We included all patients with primary parotid gland neoplasms while patients who underwent parotidectomy for metastatic tumors, inflammatory conditions or other reasons were excluded. To evaluate characteristics predictive of primary parotid malignancy, patients with primary parotid neoplasms were divided into benign and malignant subgroups.
2.2
Statistical analysis
Statistical analyses were performed with the goal of identifying patient or tumor characteristics that were associated with the diagnosis of primary parotid gland malignancy. Nature of initial patient presentation was classified into three groups: symptomatic (discomfort, facial nerve dysfunction, recurrent infection, etc.), palpable mass and asymptomatic, or incidentally noted parotid mass on imaging. A multivariate logistic regression analysis was used to compare the following variables between the benign and malignant groups: gender, lesion side, nature of presentation, and recurrence were included as categorical variables while age and tumor size were evaluated as continuous variables. More than 20% of patients did not have an available BMI, so this factor could not be included in the multivariate analysis. The multivariate analysis was performed using the procedure PROC LOGISTIC from SAS/STAT software (version 9.3), and an odds ratio with 95% confidence interval (CI) was calculated for each variable.
A two-sample t-test with equal standard deviations (univariate analysis) was carried out using Graphpad Prism v6.0d to compare mean BMI between the benign and malignant groups. This univariate analysis was also employed to compare mean tumor size between malignant tumors that did or did not recur (as well as mean tumor size for benign tumors that did or did not recur). Means and 95% confidence intervals were calculated for each variable included in these univariate analyses. For all statistical work, a p-value less than 0.05 was considered statistically significant.
3
Results
3.1
Electronic medical record review and patient selection
A total of 771 patients underwent parotidectomy at UW from 1994 to 2013, and 474 were diagnosed with a primary parotid gland neoplasm. 82.9% had benign disease (n = 393), and 17.1% were diagnosed with malignant neoplasms (n = 81). The remaining 297 patients underwent parotidectomy for different indications, most commonly metastatic squamous cell carcinoma, melanoma, or sialadenitis, and were excluded from this analysis.
3.2
Distribution of histological subtypes
As shown in Table 1 , pleomorphic adenoma (PA), Warthin’s tumor (WT), and mucoepidermoid carcinoma (MEC) were the most common neoplasms among our cohort of patients. In the benign subgroup, the next most common histological subtypes included lymphoepithelial cyst, basal cell adenoma, and oncocytoma. The other most prominent cancers in the malignant group were acinic cell carcinoma, adenoid cystic carcinoma, carcinoma ex-pleomorphic adenoma, and salivary duct carcinoma.
| Histological Subtype | Patients (n) | Percentage of all subtypes | Percentage in group (benign/malignant) |
|---|---|---|---|
| Benign Tumors | |||
| Pleomorphic adenoma | 246 | 51.9 | 62.6 |
| Warthin’s tumor | 93 | 19.6 | 23.7 |
| Lymphoepithelial cyst | 18 | 3.8 | 4.6 |
| Basal cell adenoma | 10 | 2.1 | 2.5 |
| Oncocytoma | 10 | 2.1 | 2.5 |
| Other | 16 | 3.4 | 4.1 |
| Total | 393 | 82.9 | 100.0 |
| Malignant Tumors | |||
| Mucoepidermoid carcinoma | 24 | 5.1 | 29.6 |
| Acinic cell carcinoma | 13 | 2.7 | 16.0 |
| Adenoid cystic carcinoma | 7 | 1.5 | 8.6 |
| Carcinoma ex-pleomorphic adneoma | 7 | 1.5 | 8.6 |
| Salivary duct carcinoma | 7 | 1.5 | 8.6 |
| Adenocarcinoma | 6 | 1.3 | 7.4 |
| Other | 17 | 3.5 | 21.0 |
| Total | 81 | 17.1 | 100.0 |
3.3
Patient and tumor characteristics predictive of parotid malignancy
Patient (gender, age, and BMI) and tumor (lesion side, nature of presentation, and tumor size) characteristics were evaluated to identify if a relationship existed between any of these variables and the diagnosis of primary parotid malignancy ( Tables 2 and 3 ). A greater proportion of males as compared to females comprised the malignant group (53.1% versus 46.9%) while more females made up the benign group (55.0% vs. 45.0%). Despite these absolute differences, there was not a statistically significant relationship between gender and parotid malignancy (p = 0.610). The mean BMI for patients with benign neoplasms was 29.2, and the malignant group’s average BMI was 28.1. There was not a statistically significant difference between the two groups (p = 0.196). Lastly, the age of patients with benign and malignant disease was evaluated ( Fig. 1 ). The average age was 54.4 in the benign group and 59.4 for patients with malignant neoplasms. There was a significant difference in mean age between the benign and malignant groups (p = 0.015). The odds ratio for malignant versus benign disease based on age was 1.024 (95% CI: 1.005, 1.044), indicating that patients have higher odds of malignant disease with increasing age.
| Benign | Malignant | |
|---|---|---|
| Gender | ||
| Male | 177 (45.0%) | 43 (53.1%) |
| Female | 216 (55.0%) | 38 (46.9%) |
| Nature of presentation | ||
| Symptomatic | 64 (16.5%) | 45 (56.3%) |
| Palpable, asymptomatic | 271 (69.7%) | 32 (40.0%) |
| Imaging | 54 (13.9%) | 3 (3.8%) |
| Lesion side | ||
| Right | 190 (48.3%) | 34 (42.0%) |
| Left | 203 (51.7%) | 47 (58.0%) |
| Continuous variables: Mean (95% CI) | ||
| Age | 54.4 (53.0, 55.9) | 59.4 (55.6, 63.2) |
| BMI | 29.2 (28.5, 30.0) | 28.1 (26.8, 29.5) |
| Tumor size (cm) | 2.2 (2.1, 2.3) | 2.9 (2.5, 3.2) |
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