FNA diagnostics of secondary malignancies in the salivary gland: Bi-institutional experience of 36 cases
Abstract
Fine-needle aspiration (FNA) is a key diagnostic procedure in the evaluation of salivary gland lesions. FNA is nowadays widely used in a daily clinical routine and The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) is widely accepted by the cytopathologists and endorsed by the clinicians.
Primary tumors of salivary glands are rare neoplasms. According to the Global Cancer Observatory, the incidence of primary malignancies is only 0.69 new cases per 100.000 of population per year worldwide with quite remarkable differences according to the region.
The crude incidence is the highest in Sweden with 4.9 new cases in comparison to the USA with 1.5 new cases per 100.000 of inhabitants in 2018.5 Such a low number gears up salivary gland carcinomas 30th in the ranking of the most frequent malignancies. Secondary malignancies of salivary glands (SMSGs) are even less common and represent about 5% of all salivary gland tumors (SGT).6,7 Surprisingly, there are significant differences in the percentage of SMSGs ranging from 10% to 44% of malignant tumors in the salivary glands in various regional studies.8,9,10 The majority of metastases are localized in the parotid gland and about 80% of metastases have their origin in the head and neck area.
On the other hand, metastases in submandibular gland come in 85% of cases from the areas different from head and neck being prognostically less favorable.11 Practically every malignant tumor can send metastases into the salivary glands, but the most common is squamous cell carcinoma of the skin of the head and neck area and the upper aerodigestive tract. Less common are malignant melanomas, breast, lung, and kidney carcinomas.12 Some unusual primary metastatic tumors have been also described, namely anaplastic meningioma, hepatocellular carcinoma and metastatic carcinoid.13,14,15 Immunocytochemistry (ICC) is crucial for the correct diagnosis of metastasis in the salivary gland.
It is challenging to distinguish the primary tumor without ICC. The knowledge of patient's history of malignant tumor is also a key aspect in the diagnostic work-up.6 The goal of this study was to evaluate the cytomorphological features of various secondary tumors, the spectrum of SMSGs, the role of ICC and clinical history in the diagnostics based on the experience from two tertiary care university centers in two countries.