Incidental and Non-incidental Papillary Thyroid Microcarcinoma in Denmark 1996–2015: A national study on incidence, outcome and thoughts on active surveillance

Highlights

• Papillary microcarcinoma have increased 240% in incidence in a 20 year period.

• Recurrence free survival was worse for patients with suspicion of metastasis.

• No difference in mortality was found between groups.

Abstract

Background

Incidental and non-incidental papillary microcarcinomas (PMC) are associated with different outcomes and treatment options may vary. The least favourable outcome is typically seen when carcinoma is suspected prior to surgery. Only a few studies have addressed the prognosis based on the way of detection for PMC, and they have been limited to retrospective single-center studies. We hypothesize that the “way of detection” may predict prognosis.

The aim was to calculate the incidence and outcome of PMC based on the way of detection and to identify patients that may be suitable for active surveillance.

Method

This national cohort study consists of 803 patients diagnosed with PMC in Denmark from 1996 to 2015. Patients were identified from the DATHYRCA database and allocated into groups according to the way of detection leading to surgery: Incidental at surgery (n = 527), non-incidental with symptoms suspected from the index tumor (n = 134) and non-incidental with symptoms suspected from a metastasis (n = 142).

Results

Age-standardized incidence rates increased from 0.35 per 100,000 per year in 1996 to 1.19 per 100,000 per year in 2015. A significant rise in incidence was found for both the incidental group and non-incidental group with symptoms suspected from a metastasis. Recurrence free survival was significantly worse for patients with suspicion of metastasis prior to surgery than patient groups without. No difference in mortality was found between groups.

Conclusion

PMC patients without suspicion of metastasis have the same low risk of recurrence as incidental cases and may be candidates for active surveillance.

Introduction

The incidence of thyroid cancer has increased globally over the past 40 years [1,2], with a substantial rise in the papillary subtype and in Denmark alone more than 300 patients are diagnosed each year [3,4].

When tumors of papillary thyroid carcinomas (PTC) are ≤1.0 cm in largest dimension, they are defined as papillary microcarcinomas (PMC) [5]. While PMC can be a fatal disease, the prognosis is generally favorable [6,7]. According to autopsy studies 11–36% of the population has PMC [8,9]. Despite increasing incidence, the ability to predict tumors with metastatic potential is unchanged, since diagnostic tools are dependent on post-surgical evaluation [10]. Point scores are used to predict outcome and determine treatment options, and researchers have investigated whether way of detection could predict outcome [10,11]. Currently there is no clear definition for incidental PMC. As a consequence, the proportion varies from 0% to 100% in published series [12,13]. It is generally recognized that incidental PMC has a significantly better prognosis than non-incidental [11]. The authors of a recent systematic review proposed to increase the number of groups by differentiating between whether metastasis is suspected or not [11]. Another treatment option for non-incidental PMC currently in practice in Japan and USA is active surveillance [14,15]. This option delays treatment until the cancer shows signs of significant progression to avoid overtreatment and complications associated with surgical treatment, such as recurrent laryngeal nerve paralysis or hypoparathyroidism [16,17]. This should only be considered in properly selected patients, without suspicion of metastatic disease [14].

The purpose of this study was to investigate the incidence and outcome of PMC based on the way of detection and to identify patients suitable for active surveillance.