睪丸混合性生殖細胞瘤快速增生之罕見案例報告

孫浩議¹、程威銘^1,2、張彰琦^1,2、邱逸淳^2,3

¹臺北市立聯合醫院忠孝院區外科部泌尿科

²國立陽明交通大學醫學院

³臺北市立聯合醫院陽明院區外科部泌尿科

Rapidly Enlarging Mixed Germ Cell Tumor of the Testis:
A Rare Case of One-Month Progression in a Young Adult

Hao-Yi Sun ¹, Wei-Ming Chen ^1,2, Chang-Chi Chang ^1,2, Yi-Chun Chiu ^2,3

¹ Division of Urology, Department of Surgery, Zhongxiao Branch, Taipei City Hospital

² National Yang Ming Chiao Tung University, School of Medicine, Taipei, Taiwan

³ Division of Urology, Department of Surgery, Yangming Branch, Taipei City Hospital

Introduction:

Testicular germ cell tumors (GCTs) are the most common solid tumors in males aged 15–40 and generally present as a painless, gradually enlarging mass. Rapid enlargement within a short interval is uncommon and may complicate clinical assessment ¹. Mixed germ cell tumors (M-GCTs), composed of multiple malignant germ cell components, may show variable clinical behavior depending on the proportion of non-seminomatous elements ². Recognizing such atypical presentations is essential to avoid delayed diagnosis, particularly when discomfort is mild or when clinical features mimic infection or vascular causes. We report a case of rapidly enlarging M-GCT with distinct immunohistochemical heterogeneity and excellent post-treatment outcome.

Case presentation:

A 33-year-old man with no significant medical or traumatic history presented with rapid enlargement of the left testis over one month. The swelling was initially painless but progressed from approximately 1 cm to 4 cm within two weeks, accompanied by intermittent dragging discomfort. There were no fever, erythema, urinary symptoms, or clinical signs of inflammation. Scrotal ultrasonography revealed a heterogeneous intratesticular lesion without hyperemia, prompting suspicion for a malignant rather than inflammatory etiology. Serum tumor markers were elevated, including AFP 47.42 ng/mL and β-HCG 45.5 mIU/mL, while LDH remained normal. Chest radiography was unremarkable, and contrast-enhanced CT of the abdomen and pelvis showed a 43 × 30 × 35 mm left intratesticular mass without detectable retroperitoneal or pelvic lymphadenopathy.

A left radical orchiectomy was performed. Gross pathology revealed a 3.5 × 2.5 × 2.0 cm tumor. Microscopic examination demonstrated two distinct components consistent with mixed germ cell tumor: seminoma and embryonal carcinoma. Immunohistochemistry (Figures 1–2) showed seminoma cells positive for CD117 and PLAP, and negative for CK, whereas the embryonal carcinoma areas stained positive for cytokeratin, CD30, and glypican-3, supporting the mixed histologic diagnosis. Postoperatively, AFP and β-HCG normalized. As the patient had no radiologic evidence of spread and satisfied criteria for low-risk disease, he was managed with surveillance according to IGCCCG guidelines. Over a two-year follow-up period with serial tumor markers and cross-sectional imaging, no biochemical or radiographic recurrence was detected.

Conclusion:

Rapid enlargement of a testicular mass over a short interval should prompt consideration of highly proliferative germ cell tumors, particularly when tumor markers are elevated and inflammation is absent. Mixed germ cell tumors may exhibit significant histologic heterogeneity, which can be reflected in imaging features and confirmed by immunohistochemistry. Early radical orchiectomy and guideline-based surveillance remain essential for achieving favorable outcomes. This case emphasizes that atypical rapid growth, even in the presence of mild discomfort, warrants prompt evaluation to avoid delayed diagnosis and ensure optimal oncologic control.

Discussion:

This case illustrates several clinically significant features of mixed germ cell tumors. First, the rapid increase in tumor size over a short period—enlarging from 1 to 4 cm within two weeks—is highly atypical for standard GCT presentations. Most germ cell tumors grow gradually and present as painless swelling. Rapid enlargement accompanied by mild discomfort may be mistaken for orchitis, hematoma, or torsion of the testicular appendage, potentially delaying appropriate oncologic assessment. The absence of inflammatory signs in our patient was an important clue against an infectious etiology. Similar diagnostic pitfalls in rapidly growing tumors have been described in recent series evaluating atypical GCT growth patterns ¹. Second, the concurrent elevation of AFP and β-HCG hinted at the presence of non-seminomatous components, particularly embryonal carcinoma. Embryonal carcinoma is known for its high proliferative rate and aggressive behavior, driving rapid tumor enlargement and early metastatic potential ². This biological aggressiveness likely accounted for the unusually rapid enlargement observed in our patient, even though the final tumor size remained moderate. Third, the case highlights an important imaging–pathology correlation. The heterogeneous echotexture on ultrasonography paralleled the histologic heterogeneity demonstrated on immunohistochemical staining. Seminomatous areas showed classic CD117 and PLAP positivity, while embryonal carcinoma components expressed cytokeratin, CD30, and glypican-3. For clinicians, intratesticular heterogeneity on ultrasound should raise suspicion for mixed histology rather than pure seminoma, as this distinction influences prognosis and post-orchiectomy management. Contemporary reviews emphasize this diagnostic importance of correlating imaging features with underlying tumor biology ³. Lastly, despite the aggressive biological markers and rapid clinical progression, early detection and immediate orchiectomy resulted in an excellent prognosis, with two years of recurrence-free survival. This favorable outcome reinforces the importance of timely surgical intervention and adherence to structured surveillance protocols.