The Number of Positive Lymph Nodes Instead of Extranodal Extension and Nodal Diameter is an Independent Predictor of Survival and Treatment Outcome of High-Grade Parotid Gland Carcinoma

Abstract

BackgroundThere is emerging evidence that current 8th edition of the American Joint Committee staging system is not sensitive enough to predict parotid gland carcinoma (PGC) survival outcomes. PurposeThe present study aimed to analyze pathological nodal factors related to survival and treatment outcomes in a cohort of patients surgically treated with PGC. Study Design, Setting, SampleWe performed a retrospective cohort study of consecutive patients surgically treated with PGC at the authors’ institution from January 1993 to December 2018. Inclusion criteria were as follows: confirmed high-grade parotid gland malignancy on histopathology, first surgical treatment to the parotid cancer with neck dissection with curative intent at the study clinic and sufficient data for review. Exclusion criteria were previous treatment in another institution, low-grade carcinomas, cases where neck dissection was not performed, incurable local disease and distant metastases at the time of first diagnosis and patients lost to follow-up. Predictor variablePredictor variable comprised pathological nodal factors grouped as the number of cervical node metastases, extranodal extension (ENE, largest diameter of nodal metastasis and involvement of parotid lymph nodes. Main outcome variablesOutcomes evaluated were overall survival (OS), disease specific survival (DSS), recurrence free survival (RFS), locoregional recurrence free survival (LRFS) and distant metastasis free survival (DMFS). OS was calculated from the day of biopsy or definitive surgery to the last known hospital follow-up date, or the date of death found in the hospital records or social security data. DSS was calculated from the day of biopsy or definitive surgery until the last known follow-up or death from PGC reported in the patient record. Patients who died from causes other than the disease being studied are not counted in this measurement. Treatment outcome was evaluated through occurrence of locoregional relapse of the disease or development of distant metastases. RFS was defined as the time from the date of biopsy or definitive surgery to the date of LRFS or DMFS reported in the patient record. Covariates.Covariates were composed of a set of heterogeneous variables grouped into the following categories: demographic, pathologic and clinical. Analyses.Unadjusted and adjusted hazard ratios for each variable were calculated with univariate and multivariable Cox regression. Statistical significance was defined at p value of <.05. ResultsThe cohort of 112 patients included 62 males (55%) and 50 (45%) females. The mean age of the patients was 60.52±15.22 years. The median follow-up time was 59 months (3-221 months). Adenoid cystic carcinoma was the most common tumor type with the incidence of 45%. Cumulative OS for the 5-and 10-year follow-up period was 75% and 61% respectively. Locoregional recurrences occurred with 27 (24%), distant metastases occurred with 25 (22%) and both were diagnosed with 5 patients (6%). The number of metastatic nodes was the most important nodal prognostic factor related to OS (p=0.02; HR = 2.67; CI = 0.03-6.35), DSS (p=0.011; HR = 2.55; CI = .61-6.83) and DMFS (p=0.005; HR = 2.85; CI = 0.12-4.76). Presence of pathological parotid nodes was associated with poorer RFS (p=0.015; HR = 3.45; CI = 0.25-6.02). Conclusion and relevanceNumber of metastatic lymph nodes, instead of extranodal extension and largest nodal diameter, was the contributing factor associated with survival and treatment outcomes of surgically treated patients with high-grade PGC. Since the main function of staging system is to predict outcomes, the significance of ENE and nodal dimension in salivary gland cancer staging system requires further clarification. Important finding in present study was that the presence of positive parotid lymph nodes was associated to locoregional treatment failure.