Page 36 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

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Chapter 2
Risk factors for recurrence: Margin status, age at diagnosis, and tumor location were all associated with risk of recurrence (Table 3). In patients with a reported margin status (complete cases, n=1 663), positive resection margins had an odds ratio for recurrence of 4.62 (95% CI 2.84-7.51), and 4.08 for uncertain margins (95% CI 2.24-7.43) compared to clear margins. For young age at diagnosis, the odds ratio was 0.42% (per IQR [25y]; 95% CI 0.29-0.63). Primary tumor location showed an odds ratio of 0.24 for minor salivary gland disease when compared to parotid disease (95% CI 0.07-0.77). Risk factors for malignant transformation of recurrent SGPA could not be determined, due to the low event rate (0.15%).
Missing data and imputation: Type of surgery performed and margin status were not mentioned in 42% and 21% of excerpts, respectively. There were 1 663 patients with complete information. Missing data on resection margins showed a significant association with recurrence (OR 1.5; 95% CI 1.00-2.23; p = 0.04). Taking this association into account, our analysis of imputed data with multiple- imputation models revealed the same risk factors as our analysis of complete data (Table 3).
Discussion
We report a large cohort of 3 506 patients with extended periods of follow- up and investigated SGPA incidence, recurrence, and secondary malignant transformation. Novel findings were a rising female incidence, a bimodal age distribution in women, and an overall 20-year recurrence risk of 6.7%. Positive or uncertain margins and younger age at diagnosis showed an increased overall risk of recurrence, whereas primary tumor locations in minor salivary glands showed lower recurrence.
Incidence: Direct comparisons with previous research on SGPA incidence are hard to make. In the past 50 years, crude incidence figures between 1.5 and 7.2 per 100 000 person-years [1,2,4,14–17] (Additional Table C) have been reported. However, most authors had not categorized tumors by anatomical site, and only one paper discussed national figures, which related solely to parotid SGPAs and did not standardize for age [4].