Histological reclassification of parotid gland carcinomas: importance for clinicians

Metastatic cutaneous squamous cell carcinoma accounts for nearly all squamous cell carcinomas of the parotid gland

Primary squamous cell carcinoma of the parotid gland (pSCCP) has long been recognized as a separate entity and is included in the WHO classifications of salivary gland tumors. However, it is widely accepted among head and neck pathologists that pSCCP is exceptionally rare. Yet, there are many publications describing series of pSCCP and data from SEER and other cancer register databases indicate erroneously an increasing incidence of pSCCP. Importantly, pSCCP and metastatic (secondary) squamous cell carcinoma to the parotid gland (mSCCP) have nearly identical histological features, and the diagnosis of pSCCP should only be made after the exclusion of mSCCP. Moreover, all of the histological diagnostic criteria proposed to be in favor of pSCCP (such as, for example, dysplasia of ductal epithelium) can be encountered in unequivocal mSCCP, thereby representing secondary growth along preexistent ducts. Squamous cell differentiation has also been reported in rare genetically defined primary parotid carcinomas, either as unequivocal histological squamous features (e.g., NUT carcinoma, mucoepidermoid carcinoma), by immunohistochemistry (e.g., in NUT carcinoma, adamantinoma-like Ewing sarcoma, basal-type salivary duct carcinoma, mucoepidermoid carcinoma), or a combination of both. Another major issue in this context is that the International Classification of Diseases (ICD) coding system does not distinguish between primary or metastatic disease, resulting in a large number of patients with mSCCP being misclassified as pSCCP. Immunohistochemistry and new molecular biomarkers have significantly improved the accuracy of the diagnosis of many salivary gland neoplasms, but until recently there were no biomarkers that can accurately distinguish between mSCCP and pSCCP. However, recent genomic profiling studies have unequivocally demonstrated that almost all SCCP analyzed to date have an ultraviolet light (UV)-induced mutational signature typical of mSCCP of skin origin. Thus, mutational signature analysis can be a very useful tool in determining the cutaneous origin of these tumors. Additional molecular studies may shed new light on this old diagnostic and clinical problem. This review presents a critical view of head and neck experts on this topic.

Results of histopathological revisions of major salivary gland neoplasms in routine clinical practice

AIMS

Salivary gland neoplasms are rare and are characterised by overlapping histopathological aspects. Therefore, the assessment of the correct histopathological diagnosis can be challenging. This study evaluated the frequency of pathology consultations and revisions for salivary gland neoplasms during routine clinical practice in the Netherlands. Furthermore, the concordance and discordance rates of these revisions are presented.

METHODS

The Dutch Pathology Registry (PALGA) was searched for patients that underwent a resection of a major salivary gland neoplasm between 2006 and 2016. Frequencies of pathology consultations and revisions are presented and, in order to calculate the rates of concordance and discordance, the results of the initial histopathological review were compared with the results of the revision.

RESULTS

Between 2006 and 2016, 13 441 major salivary gland neoplasms were resected in the Netherlands. 90% (n=12 082) of these tumours were diagnosed as benign and 10% (n=1359) as malignant. The initial pathologist requested a consultation in 3.3% of resections (n=439). Revision of the histopathological specimen was performed in 2.6% (n=350) of cases. Revisions were discordant in 8.3%; including 5.8% of the initially benign diagnosed lesions reclassified as malignant by the second expert pathologist and 8% of the revised malignant tumours that underwent a subtype change.

CONCLUSIONS

The number of discordant histopathological revisions (8.3%) emphasises the complexity of the histopathological diagnosis of salivary gland neoplasms. An increase in consultations may improve the accuracy of the initial diagnosis and thus treatment in salivary gland tumours while lowering the need for revisions and the number of discordant revisions.

Accuracy of parotid gland FNA cytology and reliability of the Milan System for Reporting Salivary Gland Cytopathology in clinical practice

Background

Differentiating between malignant and benign salivary gland tumors with fine‐needle aspiration cytology (FNAC) can be challenging. This study was aimed at testing the validity of the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) and at assessing possible differences in the sensitivity and specificity of parotid gland FNAC between dedicated head and neck (H&N) centers, subdivided into head and neck oncology centers (HNOCs) and head and neck oncology affiliated centers (HNOACs), and general hospitals (GHs).

Methods

The Dutch Pathology Registry (PALGA) database was searched for patients who had undergone a salivary gland resection between January 1, 2006, and January 1, 2017, and had a preoperative FNAC result. The FNAC reports were retrospectively assigned to MSRSGC categories. The risk of malignancy (ROM) was calculated for each category. The sensitivity and specificity for diagnosing malignancy were calculated and compared among HNOCs, HNOACs, and GHs.

Results

In all, 12,898 FNAC aspirates were evaluated. The ROMs for each category were as follows: 12.5% in MSRSGC I, 10.3% in MSRSGC II, 29% in MSRSGC III, 2.3% in MSRSGC IVa, 28.6% in MSRSGC IVb, 83% in MSRSGC V, and 99.3% in MSRSGC VI. The sensitivity of FNAC was highest in HNOCs (88.1%), HNOACs scored lower (79.7%), and GHs had a sensitivity of 75.0%.

Conclusions

The MSRSGC is a valid tool for reporting parotid gland FNAC; therefore, these results strongly advocate its use. On the basis of the higher sensitivity of FNAC in dedicated H&N centers, the authors recommend that GHs use the presented management strategies to help to minimize the chances of a preoperative misdiagnosis.

The Milan System for Reporting Salivary Gland Cytopathology is a valid tool for reporting parotid gland fine‐needle aspiration cytology. The sensitivity of fine‐needle aspiration cytology is higher at dedicated head and neck centers.

Salivary gland carcinoma in Denmark: a national update and follow-up on incidence, histology, and outcome

PURPOSE

Salivary gland carcinoma is a rare disease and studies on epidemiology and outcome require data collection over many years. The aim of this study is to present an update of incidence rates, anatomical sites, histological subtypes, and survival rates based on the Danish national cohort of salivary gland carcinoma patients.

METHODS

Data from all Danish patients with salivary gland carcinoma diagnosed from 1990 to 2015 (n = 1601) were included and analyzed following histological reevaluation and reclassification. Overall, disease-specific, and recurrence-free survival were evaluated. Prognostic factors were analyzed with multivariate Cox Hazard Regression.

RESULTS

The study population consisted of 769 men and 832 women, median age 62 years (range 6-102). The most frequent anatomic site was the parotid gland (51.8%). Adenoid cystic carcinoma was the most common subtype (24.7%). The majority had tumor classification T1/T2 (65.3%). The mean crude incidence was 1.2/100.000/year with an increase of 1.5% per year. There was no increase in age-adjusted incidence. The 5-, 10-, and 20-year survival rates were for overall survival 68, 52, and 35%, for disease-specific survival, 77, 69, and 64%, and for recurrence-free survival, 75, 64, and 51%, respectively. Age, high-grade histological subtype, advanced T-classification, cervical lymph node metastases, vascular invasion, and involved surgical margins had significantly negative impact on survival rates.

CONCLUSION

The age-adjusted incidence has been stable for a period of 26 years. Multivariate analysis confirmed that histological grade, advanced stage, involved surgical margins and vascular invasion are independent negative prognostic factors. Survival rates were stationary compared to earlier reports.

Nomograms predictive for oncological outcomes in malignant parotid tumours: recurrence and mortality rates of 228 patients from a single institution

PURPOSE

Malignant parotid tumours are rare and multiple prognostic factors exist.

METHODS

Through a retrospective study we aimed to identify nomograms predicting recurrence and mortality rates in 228 primary parotid cancers. Patients clinical, treatment and tumour characteristics were retrospectively collected between 1980 and 2005 at our Institution. Factors predictive of disease-free-specific-survival (DSS) and overall survival (OS) were calculated by univariate and multivariate analysis. Nomograms were then constructed.

RESULTS

The 5- and 10-year DSS rates were 73% and 71.4%, and nomogram was drawn based on five parameters where perineural invasion showed the most significant predicting influence (p < 0.001). The median follow-up was of 95 months and the 5- and 10-year OS rates were 68.7% and 53.1%; six predictive variables (age, histological grade, perineural invasion, pathological lymph node status, resection margins and distant metastasis) were used to create nomogram.

CONCLUSIONS

Our nomograms provide a tailored outcome to a patient affected by malignant parotid tumour and give him/her a risk assessment for recurrence and mortality based on individual factors by a concordance index > 0.8.

Completion surgery after extracapsular dissection of low-grade parotid gland malignant tumors

BACKGROUND

The aim of the study was to compare the oncological and functional outcome between extracapsular dissection and completion surgery on the one hand and sole extracapsular dissection on the other hand in small low-grade malignant parotid tumors.

METHODS

The records of all patients treated for T1-T2 low-grade malignant tumors of the parotid gland primarily by means of extracapsular dissection between 2006 and 2015 were studied retrospectively.

RESULTS

Forty patients with T1-T2 low-grade parotid malignancies were detected. Our study showed outstanding oncological outcomes in both patient groups, the facial nerve function being significantly better after sole extracapsular dissection in the direct postoperative phase, with no differences between the groups in the long term.

CONCLUSIONS

Our study showed very encouraging preliminary results following primary extracapsular dissection as the sole surgical therapy for carefully selected low-stage, low-grade, inferiorly located lesions in patients with high compliance.

Salivary gland carcinoma: Prediction of cancer death risk based on apparent diffusion coefficient histogram profiles

We evaluated apparent diffusion coefficient (ADC) histogram parameters for predicting the outcomes of patients with salivary gland carcinoma. Diffusion-weighted MR imaging was performed in 20 patients with salivary gland carcinoma, and ADCs were determined using b-values of 500 and 1000 s/mm². ADC histogram parameters (mean, median, percentage tumor area with distinctive ADC values [pADC], skewness, and kurtosis) were analyzed. The patients were followed for 5–136 months after primary surgery. The ADC histogram parameters and T (pT), N(pN), and M categories of the primary tumors were assessed for the prognostic importance using Cox proportional hazards models, logistic regression analysis, and receiver operating characteristic (ROC) analysis. Cohen’s d was determined for evaluating the importance of differences in the parameters between two patient groups with different outcomes. Six patients died of cancer (DOC) within 3 years after the primary surgery. Cox proportional hazards models indicated that ADC mean (95% CI = 0.494–0.977, p = 0.034), ADC median (95% CI = 0.511–0.997, p = 0.048), pADC with extremely low (<0.6 mm²/s) ADC (95% CI = 1.013–1.082, p = 0.007), kurtosis (95% CI = 1.166–7.420, p = 0.023), and pN classification (95% CI = 1.196–4.836, p = 0.012) were important factors of cancer death risk. ROC analyses indicated that the pADC <0.6 ×10⁻³ mm²/s was the best prognostic predictor (p <0.001; AUC = 0.929) among the ADC and TNM classification parameters that were significant in a univariate logistic regression analysis. Cohen’s d values between the DOC and survived patients for the ADC mean, ADC median, pADC with extremely low ADC, and kurtosis were 1.06, 1.04, 2.12, and 1.13, respectively. These results suggest that ADC histogram analysis may be helpful for predicting the outcomes of patients with salivary gland carcinoma.

Contemporary Management of Benign and Malignant Parotid Tumors

To report the standard of care, interesting new findings and controversies about the treatment of parotid tumors. Relevant and actual studies were searched in PubMed and reviewed for diagnostics, treatment and outcome of both benign and malignant tumors. Prospective trials are lacking due to rarity of the disease and high variety of tumor subtypes. The establishment of reliable non-invasive diagnostics tools for the differentiation between benign and malignant tumors is desirable. Prospective studies clarifying the association between different surgical techniques for benign parotid tumors and morbidity are needed. The role of adjuvant or definitive radiotherapy in securing loco-regional control and improving survival in malignant disease is established. Prospective clinical trials addressing the role of chemotherapy/molecular targeted therapy for parotid cancer are needed. An international consensus on the classification of parotid surgery techniques would facilitate the comparison of different trials. Such efforts should lead into a clinical guideline.

Perfusion MR imaging detection of carcinoma arising from preexisting salivary gland pleomorphic adenoma by computer-assisted analysis of time-signal intensity maps

Tumor perfusion can be evaluated by analyzing the time-signal intensity curve (TIC) after dynamic contrast-enhanced (DCE) MR imaging. Accordingly, TIC profiles are characteristic of some benign and malignant salivary gland tumors. A carcinoma ex pleomorphic adenoma (CXPA) arises from a long-standing pleomorphic adenoma (PA) and has a distinctive prognostic risk depending on the tumor growth potential such as invasion beyond the preexisting capsule. Differentiating CXPA from PA can be very challenging. In this study, we have attempted to discriminate CXPA from PA based on a two-dimensional TIC mapping algorithm. TIC mapping analysis was performed on 8 patients with CXPA and 20 patients with PA after dynamic contrast-enhanced (DCE) MR imaging using a 1.5-T MR system. The TIC profiles obtained were automatically categorized into 5 types based on the enhancement ratio, maximum time, and washout ratio (Type 1 TIC with flat profile, Type 2 TIC with slow uptake, Type 3 TIC with rapid uptake and a low washout ratio, Type 4 TIC with rapid uptake and a high washout ratio, and Type 5 TIC not otherwise specific). The percentage tumor areas with each of the 5 TIC types were compared between CXPAs and PAs. Stepwise differentiation and cluster analysis using multiple TIC cut-off thresholds distinguished CXPAs from PAs with 75% sensitivity, 95% specificity, 86% accuracy, and 86% positive and 90% negative predictive values, when tumors with ≤1.1% Type 1 and ≥15% Type 4, or those with ≤1.1% Type 1, ≥78.1% Type 2, ≥16.1% Type 3, and <15% Type 4, or those with >1.1% Type 1, ≥78.1% Type 2, and ≥16.1% Type 3 areas were diagnosed as CXPAs. The overall TIC profiles predicted some aggressive CXPA growth patterns. These results suggest that stepwise differentiation based on TIC mapping is helpful in differentiating CXPAs from PAs.