The overestimation of squamous cell carcinoma of the salivary glands – A nationwide German population based study

Introduction: Primary squamous cell carcinoma of the salivary glands (pSCC) has been described, but it must be distinguished from secondary squamous cell carcinoma (sSCC). In a previous study, we found an unusually high proportion of pSCC in the North Rhine-Westphalian (NRW) Cancer Registry. We investigated whether this finding can be observed throughout Germany and whether these tumors could be misclassified sSCC. Materials/Methods: Data on all salivary gland cancers (SGC) and cutaneous SCC (cSCC) diagnosed between 2009 and 2019 were requested from the German Centre for Cancer Registry Data (ZfKD). We estimated incidence rates of pSCC and additional cSCC and compared them between federal states. We compared the relative 5-year survival of pSCC with that of other morphologies. Results: We retrieved 10079 SGC and 927 cSCC cases from the ZfKD database. Of all SGC, 2292 (22.7%) were pSCC. The proportions of pSCC among SGC in the 16 German federal states ranged from 17.4% to 27.7%. Median age at diagnosis was 78 years (SD=12.2). The sex ratio of the age-standardized pSCC incidence rates was 3.4:1 (male:female). Primary sites of pSCC were parotid gland (84.1%), submandibular gland (12.3%), sublingual gland (1.1%) and overlapping/not otherwise specified regions (2.6%). The proportion of additional cSCC was 25.6% in pSCC patients, compared to 3.7% in adenocarcinoma patients (RR = 6.91 [95%CI 6.05, 7.89]). Relative 5-year survival of pSCC was 50.2% [95%CI: 46.1%, 54.2%]. Discussion: We found evidence for a significant overestimation of pSCC incidence in all German cancer registries. This is likely due to missing clinical information about e.g previous cSCC at the time of pathological assessment leading to misclassification of secondary tumors as pSCC.

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