Salivary gland hybrid tumour revisited: could they represent high-grade transformation in a low-grade neoplasm?
Abstrakt
Salivary gland hybrid tumour, first described in 1996, is a very rare neoplasm for which exact morphological criteriahavenotbeenuniversallyagreedupon.Incontrast,the concept of high-grade transformation (HGT) in salivary neoplasms has been widely accepted during the last decade, and thenumberofreportedcasesisrapidlyincreasing.Areviewof the literature revealed 38 cases of hybrid tumour reported in 22 publications. During approximately the same time period, well over 100 cases of HGT in salivary neoplasms have been reported.Thereareimportanthistologicalsimilaritiesbetween hybrid tumours and salivary tumours with HGT.
In the latter, containing one tumour component of low-grade malignancy and the other of high grade, the two tumour components are notentirelyseparatedandappeartooriginateinthesamearea. Virtually, all cases reported as hybrid tumour had no clear lines of demarcation between the two tumour types.
We are inclinedtosuggestthatmostofthe38casesofhybridtumours describedintheliteraturewouldtodaybetterbecalledtumour with HGT rather than hybrid tumour. The relative proportion of the two components may vary, and the high-grade component is sometimes very small, which emphasises the importanceofverygeneroussamplingofthesurgicalspecimen.The molecular genetic mechanisms responsible for HGT, including what used to be called hybrid tumour, remain largely unknown.Abnormalitiesofafewgenes(includingp53,C-MYC, cyclinD1,HER-2/neu)havebeendocumented.Asinsufficient data exist on gene abnormalities in these lesions, conclusions as to whether or not they have a common origin and which mechanisms are involved in transformation cannot be drawn.
Due to the small number of cases reported, many of which lack follow-up details; indicators of prognosis of hybrid tumours are not available, but their behaviour seems to be similartothatoftumourswithHGT,i.e.anacceleratedaggressive course.