This study aimed to provide a comprehensive description of racial differences among TC patients in the United States. Previous studies described racial differences among other cancer patients, such as melanoma [23], bladder cancer [24] and so on, but no research focus on racial differences among TC patients. According to our analysis, there were significant racial differences in patient characteristics, clinic pathologic features, incidence and survival. These results may be of use to cancer epidemiologists, clinicians, and individuals and institutions interested in developing effective policies for TC treatment and prevention.
When compared to previous literature, our findings are similar to earlier reports regarding age at diagnosis, tumor grade distribution, and TC incidence rates [2, 5, 25,26,27,28]. Furthermore, our statistical analyses suggest the existence of racial differences in the distributions of gender, marital status, age at diagnosis, survival time, histologic type, stage, treatment, tumor size, nodal involvement, and tumor location among TC patients. These observed differences may reflect differences in the timing of malignant tumor diagnoses, and the importance of early detection.
A few previous publications have also studied racial differences in TC incidence [20, 29, 30]. Chia et al analyzed data from the Cancer Incidence in Five Continents study, including age-standardized incidence rates over successive 5-year time periods with data from populations in the Americas, Asia, Europe, and Oceania [31]. They found that testicular cancer incidence remained highest in northern European populations (8.0–9.0 cases per 100,000) and lowest in Asian and African populations (< 1 case per 100,000). Our analysis includes a large, racially diverse population, and therefore has the potential to generate more comprehensive results. NHWs had the highest incidence rates of TC among the four major racial groups, while blacks had the lowest. Previous studies have reported on the association between some risk factors, including cryptorchidism, history of testicular cancer, and family history of testicular cancer, and the incidence of testicular cancer [32, 33]. However, it remains unclear why the incidence of TC among APIs and blacks is so much lower than that observed among whites. Possible explanations include differences in genetic factors, lifestyle or cultural factors, environmental factors, and variability in hormone exposures. For example, a previous study found that the level of estradiol in black pregnant women is higher than that in whites, but the increase in testosterone levels was even more significant [34]. Furthermore, the ratio of estradiol to testosterone was significantly lower in blacks compared to whites. Therefore, differences in hormone levels between pregnant women in different races may be a source of differential exposure across racial groups, thereby influencing TC risk. In addition, a case-control study of diet and testicular carcinoma found that higher total fat consumption was borderline significantly associated with increased mixed germ cell tumor risk [35]. Similarly, heterogeneity in the dietary structure of different races may also be a contributing factor to the observed differences in TC incidence. In the Western diet structure, fat intake is relatively high, accounting for 39% (35 to 45%) of total calories. However, in the Eastern diet structure, fat only accounts for approximately 20% of total calories, which may help explain why the incidence of TC among whites is higher than that of other racial groups. Previous study on dietary structure have shown that black people’s dietary structure is lower than white people’s in terms of fat intake, and the sweets/fat dietary pattern were more likely to be male, White, with lower education and income [36].
Previous publications have also reported on the racial differences of TC patients with respect to survival outcomes [37,38,39]. Bridges et al conducted a 14-year review of 215 consecutive American patients with testicular cancer and calculated the actuarial 5-year survival rates at 88% in white patients and 71% in black patients [40]. Judd et al found that race was significantly associated with testicular cancer death, with non-Caucasian men being 1.69 times more likely to die of testicular cancer than Caucasians on univariate analysis. Historically, non-Caucasian race has been associated with poorer outcomes from testicular cancer [41]. In the current analysis, we observed that whites had the highest survival rates, while blacks had the worst survival rates; suggesting that white men had a survival advantage over other races. Also consistent with the previous reports, we found that the survival rates among HWs and APIs were quite similar to one another (92.2 and 91.8%, respectively). The observed differences in survival may be due to cultural attitudes regarding malignancy, and/or knowledge and perceptions around cancer screening. At the same time, access to health care and the dissemination of health information are also potentially subjective explanations for why the survival rates of whites are higher than that of blacks [42]. Previous study found that for testis tumor treated at the same institution, there was an increased delay of diagnosis in blacks compared with whites, and the incidence of this tumor in blacks does not appear to be increasing [43]. Another study also compared prognostic data between Asians and whites, finding that Asians had lower survival rates, possibly as a result of diagnostic and therapeutic differences [44].
In our study, we found the age at diagnosis was significantly different across racial groups. HWs had the youngest age at diagnosis (30.8 years) and NHWs had the oldest (36.9 years). Several explanations may account for the racial differences observed in the current study and in previous reports [19, 45, 46]. For example, race-specific perceptions of disease, differences in socioeconomic status, the availability of health knowledge, and differences in health care accessibility may lead to differences in disease detection and may influence treatment options. When diagnosed at a localized or regional stage, TC prognosis is usually good, with survival rates as high as 95%. As noted elsewhere, with continued improvements in TC treatment, the therapeutic response of early testicular cancer is extremely favorable [47]. However, in patients diagnosed with distant stage TC, the five-year survival rates drop dramatically, particular among blacks (72.5%). These findings further highlight the importance of early detection.
There are also a few publications that have studied tumor location of TC with respect to cancer incidence and prognosis. According to these studies, undescended testis is a risk factor for TC and is usually treated surgically, but whether the age at treatment has any influence on risk remains unclear [48]. In this study, we analyzed the connection between survival rates and tumor location. When stratified by tumor location, TC in the descended testis is much more common than that of undescended testis. NHWs have the highest survival rates (96.7%) for TC in descended testis whereas API have the best survival rates (95.8%) for undescended testis. The racial differences were significant for all tumor locations. The causes of these differences are not clear at present, and therefore require further study.
We also observed significant difference among race groups according to TC treatment strategy. For patients receiving chemotherapy alone or combined chemotherapy and radiation, the treatment efficacy among NHWs is obviously superior to that observed among APIs and blacks. For radiation alone and combined surgery and radiation, HWs had the best survival rates, while for chemotherapy alone, or chemotherapy in combination with surgery or radiotherapy, NHWs had the highest survival rates (90.7, 85.6, and 63.5%, respectively). In general, the treatment of testicular tumor is divided into surgical treatment, radiotherapy alone, chemotherapy alone, and combined treatment [49]. Once identified as a testicular tumor, radical testicular resection should be performed first, and further treatment should be decided upon according to the results of the subsequent pathological examination. The diverse treatment regimens may have important impacts on prognosis, while at the same time, racial differences in post-treatment survival may result from differences in health status and the presence of comorbidities. The landmark findings detailed in the Secretary’s Task Force Report of Black and Minority Health in 1985 [50] revealed significant differences in access to medical care by race and ethnicity within certain disease categories and by various types of health services. Adherence of blacks and APIs to post-operative review and follow-up regimens is not as high as that of whites, which requires further study, alongside other potential explanations for the observed racial differences in survival.
We used the SEER database for analysis since it is currently the longest-serving cancer registry in the United States. The data of SEER registry showed that White, Black, Asian and Hispanic cover 33.6, 34.7, 62.6, and 46.7% of the respective ethnic population [51]. The proportion of Asian is a little higher than other ethnic groups, but we don’t think it affected the results according to the huge sample size. However, there are some limitations inherent in this data. First, since data is initially collected at multiple sites by several individual registries, there is the potential for administrative errors in the recording of tumor classification and staging. However, since we do not expect these types of errors to be systematic or correlated with ethnicity, any impact on our findings is likely to be relatively modest. Second, while SEER represents a large, population-based dataset, the information provided may still be inadequate for analyzing some aspects of tumor biology. For example, the lack of data on genetic factors preclude the possibility of analyzing disease subsets with distinct genetic etiology, or the impact of gene-environment interactions on TC risk and prognosis. In addition, the information on ethnicity and geographical origin is relatively cursory, and relies on self-report. Moreover, treatment selection can be affected by many factors not measured in the dataset, including insurance status, treatment availability, and others. Also, the SEER data only contain information on patients from the United States, the proportion of various ethnic groups on SEER data is basically as same as that of the 2010 U.S. Census [50]. So we think the results will represent the TC epidemiology situation in the United States. But it is not clear whether the results of this study would hold true for other regions. In addition, although the sample size is at the same level as in related studies [38, 52], it would possible be over powered.
