Page 155 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

New epidemiological and PSMA-expression based insights in salivary gland tumors
Chapter 1:
Humans have three pairs of major salivary glands and about a thousand minor glands spread out in the airways and digestive tract. These glands produce saliva which is important for several biological and mechanical functions. Saliva helps in digestion, moistening and lubrication of food, prevention of dental decay and wear, killing of microorganisms such as bacteria and viruses, protection against chemical agents and dehydration. It also plays a role in hemostasis, and woundhealing.
The salivary glands contain many other anatomical structures such as lymph nodes and lymph vessels, blood vessels and nerves. The facial nerve, which controls the muscles of facial expression and runs through the parotid can make surgery of particularly this gland challenging.
Salivary gland tumors are rare tumors. In around 85% these tumors are benign, but malignant salivary tumors also occur. The most frequent salivary gland tumor is the salivary gland pleomorphic adenoma (SGPA). This tumor has a diversity of morphological presentations with a varying combination of different cell types (epithelial, myoepithelial and mesenchymal). The SGPA sometimes turns into a malignant tumor, called the carcinoma ex pleomorphic adenoma (CEPA) despite is benign background. The malignant salivary gland tumors have a surprising wide range of histological presentations. The 2017 classification of the world health organization (WHO) mentions 20-25 different primary salivary gland cancers. These tumors have malignant characteristics such as invasive growth, mitotic figures and necrosis and genetic mutations.
Conventional imaging modalities (ultrasound, CT, MRI) show the major salivary glands in various detail. In tumor diagnostics, MRI depicts tumors best. However, these modalities have never allowed visualization of minor salivary glands. The salivary glands are now visible on nuclear scans with prostate specific membrane antigen for patients with prostate cancer (PSMA PET/CT), although possibilities for head and neck cancer have until recently not had any attention.
Because of the interesting nature of salivary glands and salivary gland tumors, this thesis will explore a main topic in both fields: epidemiology of salivary gland tumors and imaging of the salivary glands by PSMA PET/CT.
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