Aims: To estimate the proportion of de novo lacrimal gland pleomorphic adenomas (PAs) and carcinomas expleomorphic adenomas (CEPAs), together with age at presentation and first symptom. Conjectural models of tumor growth are considered.
Methods: Retrospective review of patients with orbital lobe PA or CEPA. The presenting age was examined for conformation to a Gaussian distribution and the cumulative distribution function derived for both tumor types. The risk of CEPA with age was estimated by logistic regression.
Results: About one-sixth (27/172; 16%) of these primary orbital lobe tumors were CEPAs, with 145 PAs (76/145 male; 52%) and 27 CEPAs (12/27 male; 44%). The mean presenting age for PAs was 48.3 years (median 47.7; range 11-84 years) and 57.7 years for CEPAs (median 61.2, range 27-91 years) ( p = 0.0062), and the standard deviations for each group are almost identical (16.3 for PAs, 15.9 for CEPAs; p = 0.92). Five (3.4%) PAs and 1 (3.7%) CEPA were asymptomatic: otherwise, the median symptom duration was 24 months for both PAs and CEPAs ( U test: p = 0.65). The odds of CEPA rises significantly with age, increasing 1.04-fold annually ( p = 0.0079).
Conclusion: The almost identical measures of dispersion for the presenting ages of PA and CEPA suggests that, once malignant transformation occurs, there might be a relatively constant period before it is evident. CEPAs present about a decade after PAs, this unexpectedly later presentation for the malignancy possibly being explained by a gradual replacement of the PA by the newly arising carcinoma within the preceding benign tumor.
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