Page 56 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

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Chapter 3
literature review was not sufficient to substantiate or refute consequences of RT for the risk of MT development [8,11,22]. However, a recent systematic review by McLoughlin et al found a benefit of RT in RPA and no increased risk of MT in the available evidence, that (similar to our review) lacks RCTs [38]. Overall, RT administered to especially a young patient population is known to carry inherent side-effects and a theoretical, but yet unobserved MT-risk which have to be balanced against treatment benefits. The most important benefit seems to be a lower rate of re-recurrence, with the corollary of less surgery and reduced risk to the facial nerve [13,30,31,32,39].
Historically, the threat of MT has had an important bearing on the approach to management of RPA. The reported risk of MT in PA in the literature has depended on a number of factors including patient selection, anatomical sites included, sample size, duration of follow-up and institutional selection bias which have hampered the ability to draw firm conclusions [1,2,6,18,20,23]. The present study does not provide a definitive answer as it also suffers from some of these limitations. However, from the national Dutch and Danish data it can be concluded that MT in RPA is an uncommon event occurring in at most only 0.3% (23/9,003) of patients who present with a primary PA, and around 6% in both 1st and subsequent RPA’s.
But care should be taken in accepting these figures at face value. Based on clinical experience, there is the impression that patients with MT at first recurrence and patients with MT at a later recurrence could at least partly form two different populations. Salivary gland tumor histology is notoriously difficult to interpret and it would be astonishing if there were no diagnostic discrepancies in a large series of 9,003 tumors. It is conceivable that a number of low-grade malignant tumors masqueraded as benign lumps were initially recorded as PA and their true nature became apparent at 1st recurrence (N=17). The suggestion is that (part of) these may have been malignant from the start. If correct, this would mean that the MT rate in RPA is even lower and this is the subject of a separate study currently in progress.
For the clinician managing patients with a histologically proven benign 1st RPA, the salient information is that MT is low at 2,3% (6/259) and in the present study only occurred in 6 of the 90 patients (6.6%) who failed further surgery (2-8 episodes) at mean 12.5 years follow up after the initial treatment. This is the information the patient and clinician need in order to agree a management plan suited to the individual patient.