Our study shows that the age-standardized incidence rate of thyroid cancer in Ho Chi Minh City increased appreciably in both genders during 1996-2015. The women experienced a greater incidence rate and APC than men. Regarding age at diagnosis, men were slightly older than women patients. The overall age at diagnosis appeared to decrease gradually, and the highest incidence was in the <45 years age group. Both genders shared a similar distribution of histological subtypes incidences. Papillary thyroid cancer was the most frequently diagnosed subtype and had a marked increase of 12.8-fold in age-standardized incidence rate.
The appreciably increases in the age-standardized incidence rate of thyroid cancer in Ho Chi Minh City for both genders are in accord with patterns observed in other populations over the last few decades. In China (2005-2015), the APC of overall, men, and women were 12.4, 13.3, and 10.7, respectively [9]. In Sri Lanka (2001-2010), the APC of overall, men, and women were 8.2, 5.3, and 9.0, respectively [10]. In Taiwan (1997-2012), the APC of overall, men, and women were 10.0, 9.9, and 10.3, respectively [11]. The Ho Chi Minh City figures are comparable, with the same higher trend in women than men: the APC of overall, men, and women were 8.7, 6.2, and 9.2, respectively.
There are several reasons for this upward trend in thyroid cancer incidence. Firstly, the widespread utilization of advanced diagnostic techniques could explain this acceleration rate [12],[13]. The introduction of computed tomography (CT) scan, magnetic resonance imaging, high-resolution thyroid ultrasonography, and fine-needle aspiration significantly enhanced diagnostic sensitivity. Additionally, there has been an apparent increase in medical practitioners skilled in diagnosing thyroid neoplasms in Vietnam. Secondly, it is possible that increased levels of healthcare access contributed substantially to detection improvement. Thyroid cancer incidence was significantly positively correlated with the multidimensional measures of access to healthcare [14]. As with socioeconomic status development, Vietnamese people could get to healthcare services easier and more frequently. This accessibility might be the rationale why the age at diagnosis decreased gradually since the malignancy could be detected before manifesting obvious symptoms. Thirdly, the excessive exposure to radiation from the escalating use of CT scans might also increase the thyroid cancer incidence rate [15],[16]. During childhood, the neck CT examinations could increase the risk of developing thyroid neoplasms up to 390 per million exposed individuals [17]. Finally, there are some likely risk factors related to thyroid cancer incidence, such as obesity, red meat, processed food consumption, iodine intake, mental factors, and environmental pollutant [18],[19],[20],[21]. These factors should be considered in further studies to clarify their roles in the observed increase of thyroid cancer in Vietnam.
The overall men-to-women ratio of 1:4.5 in our study was reasonably consistent with other studies [1],[9],[10],[11]. The polymorphism in estrogen receptors is supposed to be the molecular factor that results in this gender disparity [22]. Estrogen can substantially increase the cell proliferation rate in thyroid cancer cell lines, encouraging thyroid dysplasia and developing to malignancy [23],[24]. Moreover, it is hypothesized that fertility drugs are potential risk factors for thyroid cancer [25]. In agreement with various published data, women patients were slightly younger than men patients at the time of diagnosis [10],[26],[27]. This difference has yet to be explained, but the women’s hormones increase during pregnancy might play a potential role. Otherwise, menstrual and reproductive factors have a weak association with thyroid cancer [28],[29],[30].
According to histological results, papillary thyroid cancer was the main driver of the overall thyroid cancer increase during 1996-2015. This pattern reflected as well with previous findings worldwide [9],[10],[11],[31],[32]. It has been postulated that this escalating trend in thyroid cancer incidence was not a real increase but an overdiagnosis of papillary thyroid cancer, particularly with small and localized tumors due to widespread advanced diagnostic techniques [12],[33]. Papillary is the most common but the least aggressive subtype in thyroid cancer since it tends to progress very slow [34]. The 5-year relative survival rates in papillary thyroid cancer cases without metastases were nearly 100% [35]. Overdiagnosis of papillary thyroid cancer could put patients in the harm of overtreatment (surgical complications, iatrogenic hypothyroidism) without really improving the overall prognostic. Besides, overtreatment would increase the healthcare burden. Due to our study’s lack of data, we need further investigations, including diagnostic techniques, tumor characteristics, treatment procedures, and mortality, to confirm the overdiagnosis hypothesis for Ho Chi Minh City’s thyroid incidence trend.
Our study has some limitations. Firstly, there are incomplete data collections of diagnostic techniques, tumor characteristics (size, stage), treatment procedures, and mortality, limiting the full comprehension of the thyroid incidence trend. Secondly, the Ho Chi Minh Cancer Registry data did not include information on relevant characteristics, including socioeconomic status, menstrual and pregnancy factors, BMI, diet, environmental factors, and family history, preventing us from assessing specific discrepancies and risk factors. Nonetheless, the Ho Chi Minh Cancer Registry constitutes a comprehensive thyroid cancer database of all hospitals in Ho Chi Minh City for decades. Its coverage could represent of thyroid cancer database in the South of Vietnam.