Squamous cell carcinoma of the parotid gland: A population-based registry study of primary versus metastatic disease.

INTRODUCTION

Primary squamous cell carcinoma (SCC) of the parotid gland is considered exceedingly rare, yet cancer registry data from parts of Germany report unexpectedly high proportions. This raises concern that some tumors recorded as primary parotid SCC may represent secondary disease arising from earlier squamous cell carcinomas of the head and neck (SCCHN).

METHODS

We conducted a nationwide, population-based study using individual-level data from the German Centre for Cancer Registry Data (ZfKD) for 2009-2022. Parotid gland cancers were identified using ICD-10 codes, and prior SCCHN using ICD-O-3 morphology and topography codes. We analyzed incidence patterns, relative survival, diagnostic intervals, and the association between prior SCCHN and parotid cancer histology using logistic regression adjusted for age and sex.

RESULTS

Among 12,021 parotid gland cancer cases, 2767 (23%) were classified as SCC. Patients with SCC-type parotid cancer had substantially higher odds of a prior SCCHN compared with patients with non-SCC parotid cancer (adjusted OR 5.48; 95% CI 4.59-6.57). The median interval between SCCHN and parotid cancer diagnosis was 365 days for SCC-type tumors and 303 days for non-SCC tumors. Five-year age-standardized relative survival was lower for SCC parotid cancer than for non-SCC parotid cancer.

CONCLUSION

Our findings suggest that a considerable proportion of parotid SCCs recorded as primary tumors may represent misclassified secondary disease.