Differentiated Thyroid Cancer in Asians.

Abstract

In the past two decades, thyroid cancer has rapidly increased around the world, including in Korea [1]. Although the exact cause of this increase is still under debate, cancer screening with high-resolution ultrasound (US) might have led to earlier diagnosis of smaller thyroid cancers [2,3,4]. However, the increased incidence across all tumor sizes suggests that a higher rate of detection of small tumors is not the sole explanation and that other explanations, including environmental influences and molecular pathways, should be explored [5]. Differentiated thyroid carcinoma (DTC) accounts for most thyroid cancers and is characterized by an indolent tumor and a good prognosis. However, DTC may cause death in rare cases, even decades after diagnosis. Therefore, long-term follow-up is necessary [6,7] Cancer incidence disparities exist among specific ethnic populations. Several epidemiological studies in Asian-American populations reported that thyroid cancer rates were relatively high among Filipinos compared to in other Asian subgroups and non-Hispanic whites, although the reasons for this were unclear [8,9,10,11]. In addition, among this population, DTCs had a more aggressive and recurrent nature [12]. However, all of these studies were conducted in Filipinos living abroad in the United States and Canada. Considering this, Lo et al. [13] retrospectively reviewed the clinicopathologic characteristics and prognosis of 728 DTC patients at Philippine General Hospital. The authors reported that the majority of cases occurred at a younger age (<45 years) and most tumors were relatively large (between 2 and 4 cm). In addition, this study showed that papillary thyroid cancer (PTC) among Filipinos had a higher rate of distant metastases at presentation and a higher recurrence rate, suggesting more aggressive and recurrent behavior. The authors analyzed the clinical features and recurrence rate compared to other Asian populations, including Koreans. These same authors previously reported risk factors for DTC recurrence in Filipinos at Philippine General Hospital [14]. In this issue, this study was conducted retrospectively in a single institutional cohort over 15 years. Despite the long duration, the total number of DTC patients was small and the follow-up duration was relatively short. Unfortunately, most patients presented with a slowly enlarging goiter and a large mean tumor size because of limited access to medical care. Some thyroid cancers may not cause symptoms until after they reach an advanced stage. These factors may result in a high incidence of distant metastasis at presentation and a high recurrence rate. Well-known poor prognostic factors for DTC include old age, large primary tumor size, extrathyroidal extension, nodal metastasis, and distant metastases [15]. Surprisingly, fine needle aspiration (FNA) biopsy as an initial histologic test for PTC exhibited very low sensitivity because most FNA procedures were performed blind, without US guidance. US-guided biopsy of suspicious thyroid nodules may be necessary to improve reliability of FNA for thyroid nodule. Although further studies with a large sample size and genetic studies are warranted to explore the innate aggressiveness of thyroid cancer in Filipinos, timely and accurate diagnosis using US-guided FNA along with early treatment strategies should be priorities for reducing initial distant metastasis and recurrence. Considering recent issues of an epidemic of diagnosis and major harm of early detection for thyroid cancer in Korea, this study may serve as a cautionary message regarding the risks related to delayed diagnosis and treatment of DTC.