The Clinical Significance of Seminoma Component in Testicular Mixed Germ Cell Tumour

Testicular cancer accounts for nearly 1% of the tumours identified in men. It is the most commonly encountered solid malignancy in men between the ages of 15 and 35 years [1]. Primary testicular tumours can originate from germ cells, sex cord cells or, less commonly, from peritubular stromal and haematopoietic cells [2]. More than 90% of testicular cancers are malignant and originate from the germ cells. These germ cell tumours are divided into 2 main groups: seminomas and non-seminoma germ cell tumours (NSGCTs). NSGCTs represent various groups of neoplasms, including embryonal carcinomas, yolk sac tumours, choriocarcinomas, teratomas as well as mixed tumours containing the aforementioned types of tumours at varying degrees.

Mixed germ cell tumours (MGCTs) contain multiple non-seminoma components. Cases that show seminoma content along with non-seminoma components are still classified as MGCT, even if the seminoma is the main component [3]. Pure seminomas have usually excellent prognosis, in rare cases the prognosis may be poor. However, there is limited information in the literature regarding the impact of the presence of a seminoma component on MGCT prognosis.

In the present study, a 10-year series was retrospectively scanned to examine the clinicopathological characteristics, prognosis and tendency to metastasise of all MGCTs and those having a seminoma component.

A total of 221 testicular cancer cases that underwent radical inguinal orchiectomy between 2008 and 2018 were retrospectively scanned at our clinic, which was previously a military hospital and is considered as a reference centre for testicular cancer. Of these cases, 143 consisted of NSGCTs. Of the 221 patients, only 111 with fully accessible data were included in the study. The study was approved by the clinical ethics committee.

The following patient information was examined: age, complaints at admission to our clinic, primary tumour localization, primary tumour size, preoperative testicular tumour markers, MGCT histopathological components and percentages, lymphovascular invasion (LVI), pathological tumour stage, postoperative testicular tumour markers, presence of lymph node involvement in abdominal tomography, lung metastasis based on thorax tomography, clinical tumour stage, adjunctive therapies performed, state of recurrence and survival. The histopathological examination of all patients was performed by a uropathologist experienced in testicular tumours. The patients were examined after being divided into 2 groups, one of which consisted of MGCT cases without a seminoma component (group 1), while the other consisted of MGCT cases with a seminoma component (group 2).

Group 2 was also divided into subgroups according to rate of seminoma components. For the assessment of occult metastatic disease, the cut-off level of the seminoma rate in MGCTs was set at 30%. Thus, homogeneity of patients with MGCT that contain a seminoma component was provided and defined as a cut-off level like in embryonal carcinoma (>50%) that was described in the European Association of Urology guidelines.

The data were analysed using PSPP and Microsoft Excel 2010. The statistical methods used to analyse the study data included descriptive analyses (frequency distributions, percentage, average and standard deviation median); the Kruskal-Wallis H test and Mann-Whitney U test to measure the difference between the groups and the χ² test to reveal the differences between discrete variables. The results were evaluated with a confidence interval of 95% and according to a significance level of p < 0.05.

The total 111 MGCT patients who were included in the study consisted of a group of 68 MGCT patients that lacked a seminoma component (group 1) and another group of 43 MGCT patients that showed the presence of a seminoma component (group 2). The mean follow-up period was 45.06 (min.–max. 6–113) months, and 2 patients passed away during this period because of testicular cancer.

The mean age was 24.51 ± 4.79 (18–41) years, and the age distribution was 24.24 ± 4.63 years for group 1 and 25.41 ± 4.97 years for group 2. There was no statistically significant difference between the groups in terms of age and the distribution of the tumour localization (p > 0.05). The most common complaints of the patients at admission were swollen testicle (31.5%), palpable mass (30.6%), pain and swelling (19.8%) and pain (16.2%), while the testicular tumour was detected incidentally in 1.8% of the patients. The difference in the initial complaints between the groups was found to be statistically significant (p < 0.05) (Table 1).

The tumour size measured in the scrotal ultrasound performed before orchiectomy was 39.24 ± 19.26 mm. The minimum and maximum tumour sizes measured with scrotal ultrasound were 7 and 105 mm, respectively. The difference between the groups was not statistically significant (p > 0.05) (Table 1).

Tumour markers (α-fetoprotein, β-human chorionic gonadotropin and lactate dehydrogenase) on postoperative day 7 were found to be positive in 65 (58.6%) patients and negative in 46 (41.4%) patients. Individual examination of each group revealed that the postoperative positivity for tumour markers was 29 (42.6%) for group 1 and 17 (39.5%) for group 2. The difference between the 2 groups was not statistically significant (p > 0.05) (Table 2).

The contrast-enhanced tomography of the abdomen performed within the first 30 postoperative days identified a lymph node of 10–20 mm in 28 (25.2%) patients, a lymph node of 21–50 mm in 22 (19.8%) patients and a lymph node of >50 mm in 8 (7.2%) patients, while 53 (47.7%) patients did not have any lymph node involvement at all. The difference between the 2 groups was not statistically significant (p > 0.05) (Table 2).

In the clinical staging performed for all the MGCTs, it was determined that 51 (45.9%) patients were stage I, 39 (35.1%) were stage II and 21 (18.9%) were stage III. In group 1, it was found that 35 (51.4%) patients were stage I, 21 (30.8%) were stage II and 12 (17.6%) were stage III; while in group 2, it was found that 16 (37.2%) patients were stage I, 18 (41.8%) were stage II and 9 (20.9%) were stage III. The difference between the groups was not statistically significant (p > 0.05). A total of 5 patients were identified as having metastasis in other organs, with 3 patients (2.7%) having lung metastasis, 1 patient (0.9%) having brain metastasis and 1 patient (0.9%) having metastasis in the skeletal system.

MGCTs with a seminoma component were also divided into 2 subgroups, with 1 group including cases that had a histopathological seminoma component rate of 30% and higher (n = 17) and the other group including cases that had a histopathological seminoma component rate of <30% (n = 26). These 2 groups were then compared in terms of mean age, main initial complaint, size of tumour, postoperative testicular tumour markers, lymph node involvement (based on the abdominal tomography findings), lung metastasis (based on the thorax tomography findings) and LVI rates. The mean age, palpable mass, rate of lymph node involvement, rate of lung metastasis and rate of LVI were found to be higher in patients with a seminoma component rate of 30% and higher, while the mean size of the tumour and postoperative testicular tumour markers were found to be lower. No statistically significant difference was identified between these 2 groups (p > 0.05) (Table 3).

In group 1, 15 (22%) of the 68 patients underwent primary retroperitoneal lymph node dissection (RPLND). Of these 15 patients, 3 (20%) had live tumour cells, 1 (6.6%) had teratoma, and 2 (13.3%) had live tumour cells and teratoma simultaneously. In group 1, 19 (27.9%) of the 68 patients underwent RPLND following chemotherapy. Among these 19 patients, 9 (47.3%) had teratoma and 3 (15.8%) had live tumour cells. In group 2, 6 (13.9%) of the 43 patients underwent RPLND. Two of these 6 patients had live tumour cells and teratoma simultaneously. In group 2, 10 (23.2%) of the 43 patients underwent RPLND after chemotherapy. Five of these 10 patients (50%) had teratoma, while 4 (40%) had live tumour cells. Statistical analysis was not performed due to the small cohort of included patients that underwent RPLND.

The histopathological, demographic and clinical data for the 43 MGCT patients having a seminoma component are summarised in Table 4. The cases were followed up for an average period of 36.2 months, and 37 of these cases did not exhibit recurrence during this follow-up period. During the follow-up period, 3 patients presented late retroperitoneal recurrence, and 1 patient had late brain metastasis. During the follow-up period, 1 other patient also passed away because of testicular cancer.

Testicular tumours are a heterogeneous group of neoplasms that present different histopathologies and variable clinical courses and prognoses. Tumours that originate from the germ cells account for nearly 95% of all testicular cancers [4]. According to the available literature [5], MGCTs are the second most common testicular germ cell tumours after seminomas and account for 40–45% of all the primary testicular GCTs. The reason why MGCTs are this common may be linked to the fact that germ cells in the testicles are totipotent and undergo trophoblast or somatic differentiation. In the primary tumours or those that are metastatic, potent types of NSGCTs can transform into other NSGCT types [3]. The strong similarity between seminoma and intratubular germ cell neoplasia supports the hypothesis that seminoma is a precursor of other GCTs. According to this hypothesis, seminoma can differentiate and transform embryonal carcinoma and yolk sac tumours into MGCTs [6]. The same also applies to embryonal carcinomas, which, owing to their pluripotent nature, can transform into other NSGCTs and MGCTs such as teratomas, yolk sac tumours and choriocarcinomas through somatic differentiation [7]. Although the presence of seminomas within MGCTs is not generally considered as a negative prognostic factor, there are, as of yet, no published/reported studies on this topic in the literature [8].

In a study conducted by Miyai et al. [9] in 2018, it was reported that MGCTs containing a seminoma component exhibited genetic variations that were different from the ones observed in pure seminomas. Loss of heterozygosity was reported to be more frequent in MGCTs that had a seminoma component, and part of this loss of heterozygosity was reported to be associated with a loss of protein expression (i.e., PTEN). In the same study, a high level of allele losses was observed on the specific chromosomal loci of MGCTs that contain a seminoma component (i.e., 6p and 10q). The conclusion from this study was that although the word “seminoma” may initially suggest a good prognosis, the involvement of the seminoma component in MGCTs is not a good prognostic factor. Furthermore, considering the hypothesis that seminoma component in MGCTs is a precursor of other GCTs, it can be presumed that because MGCTs with a seminoma component have a high number of genetic anomalies, they can progress with greater malignancy.

In the light of these findings, the presence of seminoma in MGCTs should be evaluated clinically. With regard to age of the patients diagnosed with a testicular tumour, a bell-shaped curve of 10 years has been reported between seminomas and NSGCTs [10]. There was no clear relationship between the presence of seminoma in MGCTs and the age at diagnosis of the patients with MGCT in the literature. Only 1 study in the literature that separately examined MGCTs depending on whether they contained a seminoma component was reported. According to this study, the mean age of patients with MGCTs that lacked a seminoma component was reported as 29 years, while the mean age of patients with MGCTs that had a seminoma component was reported as 25 years [11]. However, the said study performed no statistical analysis between these 2 groups. The reason why no statistical analysis was performed between the 2 groups could be associated with the relatively small number of patients included. The number of patients with MGCTs that lacked a seminoma component was 30, while the number of patients with MGCTs that had a seminoma component was 19. The same study also reported that compared with MGCTs, pure seminomas were observed in patients who were statistically significantly older (the mean age was 34 years for pure seminomas and 27 years for MGCTs) [10]. In our study, the mean age of group 1 at the time of orchiectomy was 24.2 years, while the mean age of group 2 was 25.4 years, and this difference was not found to be significant (Table 1). However, as the seminoma component in MGCTs increases, the age of diagnosis of the patients with MGCTs increases. In our study, while those with a seminoma content below 30% behaved like the classic MGCT cases, when the seminoma rate was higher than 30%, it exhibited a non-seminomatous behaviour. It is also seen at an early age and is aggressive. These findings were found to be concordant with Albers et al.’s [6] theory. Some seminomas have an aggressive behaviour and ability for differentiation at the cellular level. This condition supports their conversion to MGCTs, which is more frequently detected at an early age.

LVI in the primary tumour has been shown to robustly identify a group at higher risk of relapse [12]. Some studies have suggested that pure embryonal histology has significance, although it is less strongly associated with relapse than LVI [13]. However, there is limited information in the literature regarding the impact of the presence of a seminoma component on the disease prognosis. As is the case with other germ cell tumours, the rate of tumour spread in the retroperitoneal space is 70–80% [8]. Scanning for metastases after orchiectomy in the present study revealed that the rates of clinically significant lymph node involvement and lung metastasis in the patient group with MGCTs having a seminoma component were higher than in group 1. However, these differences were not statistically significant. In the clinical staging of both groups, 16 (37.2%) patients with MGCTs having a seminoma component were determined to be at stage I, while this figure was 35 (51.4%) in the other group. It has been reported in large case series that 55% of MGCTs were stage I, although there is no detailed information regarding the presence or absence of the seminoma component in them [14]. However, in the group of patients we studied, advanced stage (stages II and III) was identified more frequently in MGCTs that contained a seminoma component than in MGCTs that lacked a seminoma component.

It is reported that in NSGCTs, pathology evaluations for RPLND performed following chemotherapy revealed live tumour cells at a rate of 6–10%, mature teratomas at a rate of 50% and necrotic-fibrotic tissues at a rate of 40% [15]. Another aspect that needs to be emphasised in the present study is that the RPLND pathology evaluations performed primarily and following chemotherapy revealed higher rates of live tumour cells in the group of patients with MGCTs having a seminoma component.

The results of the present study show that MGCTs that include a seminoma component (especially 30% and higher) have a more advanced disease stage, greater lymph node involvement and a higher tendency for lung metastasis. The reason why these results have not been statistically supported can be explained by the low number of patients. The prognostic impact of the MGCTs that have a seminoma component should be re-examined in other case series with larger patient populations. The risk classification of the International Germ Cell Cancer Collaborative Group may undergo changes following the new studies conducted in this field [16].

The limitations of the present study included the retrospective evaluation of the data in a single centre and the lack of large patient cohorts with MGCTs containing or lacking a seminoma component. The 5-year overall survival rates of the patients could not be obtained because the follow-up period was not long enough.

Although the word “seminoma” may initially be interpreted as an indication of good prognosis, the presence of a seminoma component in MGCTs may not necessarily prove to be a good prognostic factor. MGCTs that contain a seminoma component (especially 30% and higher) can have a higher tendency for occult metastatic disease. The prognostic impact of the seminoma component in MGCTs should be re-examined in case series involving a higher number of patients.

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.

The authors declare that they have no conflicts of interest.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

S.A.: study concept and design, analysis of data, intellectual oversight, manuscript preparation and editing. C.E.: study design, provision of patients, manuscript review. H.H.T.: statistical analysis, data interpretation, manuscript review and editing. A.O.: lead statistical design, study design, provision of patients. O.Y.: administrative and logistical support, manuscript review and editing.