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Otolaryngology–Head and Neck Surgery 154(1)

many histologies by salivary gland primary site, the debate continues regarding appropriate therapy. The National Cancer Data Base (NCDB) is the largest cancer registry in the world, capturing approximately 70% of all cancer diagnosis in the United States. It is a high quality database with annual quality control checks and measures, an excellent resource for studying rare cancers. Using records from 1998 to 2012, we have identified the largest series of parotid gland carcinomas to date with aims of identifying predictive factors of regional metastasis and studying its effects on survival. Materials and Methods We conducted a retrospective review of the NCDB Participant User File from 1998 to 2012. The Medical University of South Carolina Institutional Review Board determined that this project met criteria for ‘‘not human subjects’’ research. We searched the database for all patients with a diagnosis of primary parotid gland carcinoma, using the topological ICD-O-3 code C079. Patients who presented with metastatic disease to the parotid gland and those with tumors of questionable malignant potential were excluded from this group by specific selection for histologic codes for primary malignancy. Patients were considered to have positive nodal disease if there was at least 1 positive lymph node confirmed by biopsy for nodal disease as part of diag nosis or treatment or if they had clinical evidence of nodal disease without further pathologic follow-up. World Health Organization–classified histopathologies with at least 250 cases were studied to maximize power. Data fields extracted for each case included age at diagnosis, sex, race, tumor grade, type of surgical therapy, type of radiation therapy, clinical stage, pathologic stage, pathologic lymph node involvement, follow-up duration, and survival. Currently, more robust grading systems exist only for adenoid cystic carcinoma, mucoepidermoid carcinoma, and acinar cell carcinoma. 21 Given the lack of grading standardi zation and the histologic heterogeneity, we simplified grad ing into low and high. NCDB grades of 1/I and 2/II were classified into the low-grade category, and grades of 3/III and 4/IV were classified into high-grade category. 22 We believe that this interpretation of grade effectively captures the most important grading differences for each histology while maintaining accuracy. All other data fields were coded according to the NCDB instructions. These data were then imported into SPSS 23 (IBM Corp, Chicago, Illinois) for further analysis. Categorical variables are presented as frequency and percentage. Prevalence of nodal disease was compared by factors of grade and clinical T stage via chi-square tests. Predictors of nodal disease were calculated for the variables of age, sex, race, clinical T stage, and grade. Variables that were correlated with the Spearman correlation at a significance level of 0.05 were used for regression. Univariate and multivariate binary logistic regression was conducted with an enter likelihood ratio method. Two-year overall survival (OS) and 5-year OS were the assessed outcome variables and were tabulated in

life tables. These curves were tested for significance via the log-rank test. P \ .05 was considered to indicate a statisti cally significant difference for all statistical tests. All squamous cell carcinomas (SCCs) were excluded. It is unknown how many SCCs in our data are likely regional metastasis from a cutaneous malignancy. Prior to exclusion, SCC was 14% of our histologic distribution. Primary SCC has been described to be a very rare primary parotid cancer (0.3%-3.4% relative incidence) from smaller case series that reviewed histologic data and with lesser likelihood of mis classification. 23 This percentage soars in larger population database studies (19.8%-21.2%), where authors also have cited the potential drawbacks of registry misclassification as secondary lesions. 4,13 The ‘‘other’’ category includes . 90 coded histologies composed of various sarcomas, metastatic tumors, melanoma, and other esoteric classifications, typically with \ 5 patients. These numbers accumulate significantly in our large sample, while such cases are typically excluded or nonexistent in smaller studies. Bhattacharyya and Fried’s 2005 review of 903 parotid cancers using the SEER database did not include an ‘‘other’’ category. 4 Even in Spiro’s landmark 1986 study with 1278 salivary gland cancers, ‘‘other’’ made up only 3% of their data set. 7 Our 18% relative incidence quite signifi cantly dilutes the relative incidences of other histologies, which could explain our lower numbers for mucoepidermoid carcinoma, adenoid cystic carcinoma, and adenocarcinoma not otherwise specified (NOS) as compared with those of other authors. 4,7,24 While we did include ‘‘other’’ in our OS analysis, we felt it inappropriate to conduct further survival analysis on such a heterogeneous group. We identified 22,653 patients with primary parotid malig nancy. Median age overall was 61 years, with peak inci dences between 60 and 80 years. A majority of patients were Caucasian (86%), with 10% African American and 4% of other ethnicities. No overall sex preference was seen (53% male). Most malignancies were diagnosed at early T stages (38% T1, 33% T2). A slight majority of cancers were low grade (55%). Other clinical and demographic data by histology can be found in Table 1 . While 55% of cases overall were low grade, a majority of adenocarcinoma NOS (67%), carcinoma ex pleomorphic adenoma (69%), and sali vary ductal carcinomas (79%) presented with high-grade disease. Histopathology and Nodal Disease Incidence The most common histology was mucoepidermoid carci noma (31%), followed by acinic cell carcinoma (18%), ade nocarcinoma NOS (14%), adenoid cystic carcinoma (9%), carcinoma ex pleomorphic adenoma (4%), epithelial myoepithelial carcinoma (2%), basal cell adenocarcinoma (2%), and ductal carcinoma (2%); 18% were other histologies. Results Patient Demographics and Clinical Features