Aim: To investigate the effects of changing surgical practices on thyroid cancer incidence in the Veneto Region (North-Eastern Italy).

Methods: Hospital discharge records of the period 2000-2010 were analyzed to detect trends in thyroid surgery rates by type of surgery and diagnosis. The association between surgery rates for benign and malignant diseases across the 21 Local Health Units (LHUs) was assessed by Poisson regression. In a second step, clinical and pathological charts of the year 2010 were retrieved from the larger regional surgical center. The proportions of total and incidental papillary thyroid micro carcinoma (PTMC) were compared with historical data. Factors influencing an incidental diagnosis of PTMC were analyzed by logistic regression.

Results: Among 26,000 procedures performed in the Region, there was an increase with time in the proportion of total thyroidectomies (from 67% to 78%) and surgeries with a diagnosis of thyroid cancer (from 17% to 28%). Cancer surgery rates across LHUs resulted associated to surgery rates for benign diseases (P<0.001). In the largest regional center, the proportion of PTMC increased from 35% to 56%, of whom almost 60% were incidental cases. The probability of finding an incidental PTMC was higher in total thyroidectomies than in other procedures (odds ratio=1.84, 95% confidence interval 1.08-3.14).

Conclusion: Data from the Veneto Region suggest that the increase in PTMC is due to several factors: increased preoperative diagnosis, total gland removal, extensive histological examination. Moreover, geographical variations in cancer incidence were associated to surgery rates for benign diseases.