Page 29 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

Salivary gland pleomorphic adenoma in the Netherlands
Introduction
Most salivary gland tumors are benign, with malignancy found in roughly 14% of lesions [1,2]. The most common tumor type is salivary gland pleomorphic adenoma (SGPA), which accounts for more than 70% of benign epithelial tumors. These well-circumscribed tumors with ductal and myoepithelial elements are found in both the major and minor salivary glands with most occurring in the parotid gland. They are more common in women and age at diagnosis is mostly between 40-59 years old [2,3].
The standard of treatment is nerve-conserving, superficial parotidectomy (or extracapsular dissection in well trained hands). Recurrence is reported in 0-3% of patients [4,5]. Historically, enucleation was performed but this was associated with unacceptably high recurrence rates of up to 45% [6,7]. Results of postoperative radiotherapy for recurrent SGPA, show better local control (up to 94% after 20 years follow-up) than surgery only, in retrospective series [6,8,9].
In 1.8-6.2% of cases, SGPA transforms into carcinoma ex pleomorphic adenoma[4,10]. These cases make up 7.7-11.6% of all malignant salivary gland tumors [10,11]. In recurrent SGPA, de novo malignant transformation is reported in 0-23% [6].
As common a tumor as SGPA may be, its epidemiology has long remained uncertain for lack of national registration [4,12,13]. The literature reports research focused on benign salivary gland tumors in general or subgroups of SGPA [2,14– 17]. Others have looked at regional incidence of SGPA or national incidence of parotid SGPA [1,4], but to our knowledge, national incidence of all-location SGPA and trends over time have not been investigated.
Of course, without any national data, no rates can be calculated for all-location SGPA incidence, recurrence, and secondary malignant transformation without a strong possibility of referral bias. We therefore decided to use the Dutch nationwide registry of pathology reports (PALGA). This registry is not restricted to any specific type of finding or disease, thus making a suitable database for studying SGPA epidemiology features, including trends over time.
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