Mixed Testicular Germ Cell Tumor with Five Distinct Components Arising from Germ Cell Neoplasia In Situ – A Case Report

1. Introduction and Clinical Significance

Testicular cancer is the most common solid malignancy in adolescent and young adult males, particularly between 15 and 40 years of age. Its incidence has increased over recent decades with more than 72.000 new cases globally each year, especially in industrialized countries, suggesting a relevant role for environmental, endocrine, and genetic factors in its pathogenesis [1,2]. Although it accounts for approximately 1% of all male malignancies, it is responsible for a disproportionate number of life-years lost, as it predominantly affects individuals in their reproductive years [3].

Germ cell tumors (GCTs) account for 90–95% of testicular tumors and are generally divided into seminomatous and non-seminomatous categories, based on their histopathological characteristics and clinical behavior. This heterogeneous group of histological subtypes derived from a common precursor —the germ cell neoplasia in situ (GCNIS)— may coexist within a single lesion, giving rise to the so-called postpubertal-type mixed germ cell tumor (PTMGCT), which represent approximately 30–40% of all GCTs [4,5].

Accurate identification and quantification of all histological components in a PTMGCT is not merely of academic interest but directly influences staging, risk stratification, and therapeutic decision-making. Tumors composed by five distinct histological components are exceptionally rare, accounting for <1% of all testicular GCTs [6]. In this context, we report an unusual case of a PTMGCT composed of seminoma, embryonal carcinoma, teratoma, yolk sac tumor, and choriocarcinoma in a 29-year-old patient.

2. Case Presentation

A 29-year-old man with no relevant medical history other than seasonal asthma and tobacco smoking presented with a painless nodule in the upper pole of the right testis, incidentally detected by the patient. Physical examination revealed increased consistency in the upper region of the right testis, without signs of local inflammation or involvement of the epididymis or spermatic cord. Examination of the contralateral testis was normal.

Scrotal ultrasonography demonstrated a solid, heterogeneous, hypoechoic lesion measuring approximately 2 cm in diameter in the upper pole of the right testis, with internal vascularity on color Doppler imaging (Figure 1). No sonographic evidence of epididymal or spermatic cord involvement was observed. A small adjacent satellite nodule measuring approximately 3 mm was also identified.

Serum tumor markers showed elevated β-human chorionic gonadotropin (β-hCG) levels (20.3 mIU/mL), with alpha-fetoprotein (AFP; 7.5 ng/mL) and lactate dehydrogenase (LDH; 165 U/L) within normal limits. Computed tomography of the chest, abdomen, and pelvis revealed no evidence of distant metastases or retroperitoneal lymphadenopathy, consistent with clinical stage I disease.

The patient underwent right radical inguinal orchiectomy with placement of a testicular prosthesis. Gross examination of the surgical specimen revealed a testis measuring 4.2 × 3 cm attached to an 8-cm long spermatic cord. Sectioning disclosed a firm, whitish nodular mass with focal hemorrhagic areas measuring 2 × 1.8 cm, abutting but not invading the tunica albuginea (Figure 2). Notably, a 3-mm satellite nodule was also observed.

Histopathological analysis of the orchiectomy specimen demonstrated a postpubertal-type mixed GCT composed of five distinct neoplasms within a single nodular lesion (Figure 3). Each component was morphologically and immunophenotypically consistent with its pure counterpart, and their relative proportions were estimated based on the total tumor area as follows:

• Embryonal carcinoma (60%): solid growth pattern with pleomorphic cells, prominent nuclei, and high mitotic activity; positive for CD30 and pancytokeratin (AE1/AE3).
• Postpubertal mature and immature teratoma (15%): tissues derived from all three germ layers, including keratinizing squamous epithelium, immature cartilage, and smooth muscle.
• Postpubertal yolk sac tumor (10%): glomeruloid structures consistent with Schiller–Duval bodies; AFP-positive.
• Classic seminoma (10%): large cells with clear cytoplasm, round nuclei with prominent nucleoli, and lymphocyte-rich stroma; tumor cells expressed CD117 (c-KIT) and OCT3/4.
• Choriocarcinoma (5%): hemorrhagic areas containing syncytiotrophoblastic and cytotrophoblastic cells with β-hCG expression.

Adjacent testicular parenchyma, including the 3-mm satellite nodule, demonstrated germ cell neoplasia in situ (GCNIS). No lymphovascular invasion or involvement of the epididymis or rete testis was identified.

Postoperative follow-up demonstrated progressive normalization of serum tumor markers (β-hCG <2 mIU/mL, AFP 3.4 ng/mL, LDH 145 U/L) and no evidence of local recurrence or distant disease after 18 months of surveillance.

3. Discussion

Most testicular GCT arise from primordial germ cells (gonocytes) that remain developmentally arrested and fail to differentiate into spermatogonia due to a combination of genetic susceptibility and prenatal environmental exposures (e.g., maternal exposure to estrogen-like compounds or organochlorine substances). These factors lead to dysfunction of androgen or anti-Müllerian hormone signaling pathways, resulting in the persistence of a latent totipotent developmental potential in these cells residing within the spermatogonial niche of the seminiferous tubules [7]. Epigenetic dysregulation of these cells results in transformation into germ cell neoplasia in situ (GCNIS), also known as intratubular germ cell neoplasia, which represents the common precursor of both seminomatous and non-seminomatous postpubertal-type GCT [8,9].

GCNIS may remain clinically silent for years until the acquisition of additional genetic abnormalities, most notably gain of chromosome 12p (isochromosome i(12p)), that triggers progression to invasive disease [10]. Initial differentiation typically gives rise to seminoma or embryonal carcinoma, with subsequent potential transformation into choriocarcinoma, postpubertal yolk sac tumor, or postpubertal teratoma [7,8]. Teratomas are composed of at least two embryonic germ layers —ectoderm, mesoderm, and/or endoderm— and may, in rare instances, undergo transformation into a secondary somatic-type malignancy (i.e., the development of a non–germ cell malignant neoplasm such as sarcoma, adenocarcinoma, or embryonic-type neuroectodermal tumor arising within a GCT)[5,10]. Therefore, presence of GCNIS in adjacent parenchyma supports a multifocal progressive transformation process, and justifies close surveillance of the contralateral testis in young patients at increased risk [11].

Mixed GCT may contain several components in varying proportions. However, the individual elements are histologically and immunophenotypically identical to their pure counterparts [4]. The recognition of extreme histological heterogeneity within a single PTMGCT is of paramount importance, as each component carries distinct biological behavior, metastatic potential, and response to therapy. For instance, tumors dominated by aggressive non-seminomatous elements such as embryonal carcinoma or choriocarcinoma are associated with a higher risk of early systemic dissemination, whereas teratomatous components may confer resistance to chemotherapy and require surgical management [7,10]. Nevertheless, the amount of each component also provides critical prognostic information beyond mere histological presence, as some studies have found that a ≤5% choriocarcinoma component may not significantly worsen prognosis [12].

Early diagnosis of testicular GCT relies on clinical vigilance in the evaluation of any testicular abnormality, even in the absence of pain. Diagnostic assessment includes physical examination, scrotal ultrasonography, and measurement of serum tumor markers such as AFP, β-hCG, and LDH, which are particularly valuable for post-treatment monitoring [13]. AFP is elevated in approximately 50-70% of non-seminomatous germ cell tumors (NSGCT), almost exclusively reflecting the presence of yolk sac tumor differentiation, while it is never elevated in pure seminoma [14]. β-hCG is increased in approximately 40–60% of NSGCT and in 10–30% of seminomas, typically due to syncytiotrophoblastic elements [15]. LDH, although associated with tumor burden, shows low specificity and may be elevated in a wide range of non-malignant conditions [15]. At least 60% of patients with testicular cancer present with elevation of at least one serum marker at diagnosis [15]; however, the unaltered values of AFP in our case can be explained by the limited proportion of yolk sac tumor (approximately 10%), as AFP secretion correlates more closely with the volume of AFP-producing cells rather than their mere presence, highlighting that normal markers do not exclude malignancy [16]. Overall, while marker elevation patterns often reflect the dominant tumor component, definitive classification and risk stratification requires a thorough histopathological and immunohistochemical evaluation [5,9] (Table 1).

From a clinical perspective, radical inguinal orchiectomy remains the cornerstone of initial management, allowing definitive diagnosis and pathological staging. Afterwards, follow-up with serial serum tumor marker assessment and imaging studies are essential. In patients with stage I disease, choice between subsequent active surveillance or adjuvant treatment should be based on up-to-date clinical guidelines, but also on multidisciplinary discussion and patient preference [13]. Mixed tumors with a dominant non-seminomatous component may warrant a more aggressive therapeutic approach depending on patient risk factors (e.g., lymphovascular invasion, direct invasion of the spermatic cord or scrotum), as up to 30% of patients with stage I NSGCT may relapse during the first two years (early relapses) [17]. In stage I NSGCT patients without risk factors and postoperative normalization of tumor markers, prognosis is generally favorable and active surveillance is recommended as an appropriate management [13,17].

4. Conclusions

Postpubertal mixed testicular germ cell tumors represent a biologically complex entity demanding a comprehensive clinicopathological approach that combines clinical evaluation, testicular ultrasonography, serum tumor markers, and thorough histopathological examination. This case, featuring the simultaneous presence of seminoma, embryonal carcinoma, choriocarcinoma, yolk sac tumor, and teratoma, illustrates the full malignant differentiation spectrum of GCNIS and reinforces its role as a precursor lesion and marker of bilateral disease risk, supporting careful follow-up of the contralateral testis. Accurate identification and quantification of each tumoral component are essential not only for prognostic assessment but also for guiding surveillance intensity and therapeutic decision-making.