Seminoma

01Pathophysiology

Seminoma originates from germ cell neoplasia in situ (GCNIS), formerly known as intratubular germ cell neoplasia or carcinoma in situ of the testis. GCNIS represents atypical gonocytes that failed to differentiate properly during embryonic development. These cells persist within the seminiferous tubules and, under the influence of hormonal changes at puberty, gain the proliferative potential to progress into an invasive tumor.

At the molecular level, the majority of seminomas carry isochromosome 12p [i(12p)], a gain of the short arm of chromosome 12. This chromosomal abnormality is shared across germ cell tumors and results in overexpression of genes that promote cell survival and proliferation, including cyclin D2 and KRAS. The transcription factor OCT3/4 (POU5F1) is strongly expressed in seminoma cells, reflecting their retained pluripotent germ cell identity. This marker is also useful histologically, as it stains the tumor nuclei.

The connection between cryptorchidism and seminoma deserves emphasis. The undescended testis is exposed to higher core body temperature, which impairs normal germ cell maturation and promotes the accumulation of genetic damage in spermatogonia. Even after orchiopexy (surgical correction), the risk of testicular cancer remains elevated because the germ cell damage occurred during embryonic and early postnatal development. Orchiopexy before puberty reduces, but does not eliminate, this risk.

Histologically, classic seminoma consists of sheets of uniform, large, round cells with abundant clear or pale cytoplasm and centrally placed nuclei containing prominent nucleoli. The stroma characteristically contains fibrous septae infiltrated by lymphocytes, sometimes forming granulomas. This lymphocytic reaction is thought to be an immune response to the tumor and may partly explain why seminoma has a more favorable prognosis compared to non-seminomatous germ cell tumors. The "fried egg" appearance of the cells arises from fixation artifact that clears the glycogen-rich cytoplasm.

Seminoma tends to spread in an orderly, stepwise fashion through lymphatic drainage. The right testis drains to the interaortocaval lymph nodes, while the left testis drains to the para-aortic (left lateral) lymph nodes. Hematogenous spread (to lungs, liver, bone, brain) occurs later and is less common compared to non-seminomatous tumors, particularly choriocarcinoma, which is notorious for early blood-borne dissemination.

The reason AFP must be normal in pure seminoma is critical for exam purposes. Seminoma cells do not produce alpha-fetoprotein. If the AFP is elevated, it indicates the presence of a non-seminomatous component (most commonly yolk sac tumor elements), regardless of what the histology shows. This changes the treatment plan entirely. A mildly elevated beta-hCG, on the other hand, may be seen in pure seminoma because syncytiotrophoblastic giant cells (which produce hCG) can be scattered within the tumor without changing its classification.

02Classification and Clinical Manifestation

Important exam distinction: Spermatocytic tumor is now classified separately from classic seminoma in the WHO classification. It occurs in older men and carries an excellent prognosis with no need for adjuvant therapy. If a vignette describes an older man (>50) with a testicular mass and biopsy showing three distinct cell sizes without GCNIS, think spermatocytic tumor.

Clinical Manifestation

03Diagnostic Workup

When a young male presents with a painless testicular mass, the first step is a scrotal ultrasound with Doppler. This is the best initial test because it is noninvasive, widely available, and highly sensitive for distinguishing intratesticular masses (which carry a high probability of malignancy) from extratesticular lesions (hydrocele, epididymal cyst, spermatocele), which are almost always benign. On ultrasound, seminoma appears as a homogeneous, hypoechoic mass within the testicular parenchyma, often with increased vascularity on Doppler.

Before any surgical intervention, you must draw serum tumor markers: AFP, beta-hCG, and LDH. These serve three purposes: they help distinguish seminoma from non-seminomatous germ cell tumors, they establish a baseline for monitoring after surgery, and they contribute to staging and prognosis.

The most tested rule regarding markers is this: if AFP is elevated, the tumor is not a pure seminoma, regardless of histology. AFP is produced by yolk sac tumor elements. Even if the pathologist reads the specimen as pure seminoma, an elevated AFP mandates treatment as a non-seminomatous germ cell tumor (NSGCT), because the AFP-producing component was either missed on sampling or is present in a metastatic site.

Beta-hCG can be mildly elevated (typically <200 mIU/mL) in pure seminoma owing to scattered syncytiotrophoblastic cells. Markedly elevated beta-hCG levels (>5,000) should raise suspicion for choriocarcinoma or a mixed germ cell tumor.

LDH is a nonspecific marker but is useful for staging and monitoring treatment response. It reflects overall tumor burden and cell turnover.

The next step after ultrasound confirms an intratesticular mass is radical inguinal orchiectomy. This is both the diagnostic and therapeutic procedure. The approach must be through the inguinal canal (not the scrotum) to maintain the integrity of lymphatic drainage pathways. A transscrotal biopsy or orchiectomy is contraindicated because it risks seeding tumor cells into scrotal lymphatics, which drain to inguinal nodes rather than the expected retroperitoneal nodes. This would alter the lymphatic drainage pattern and potentially change the stage and radiation field.

After orchiectomy, staging CT of the chest, abdomen, and pelvis is performed to evaluate for retroperitoneal lymphadenopathy and pulmonary metastases. Post-orchiectomy markers are rechecked. The pattern of marker decline (particularly the half-life of beta-hCG, which is 24 to 36 hours) is monitored to ensure appropriate clearance.

IGCCCG Prognostic Classification (Seminoma)

There is no poor-prognosis category for seminoma, unlike NSGCT. This reflects its overall favorable biology.

04Management and Treatment

Radical inguinal orchiectomy is the first therapeutic step for all stages. The procedure involves clamping the spermatic cord at the internal inguinal ring before mobilizing the testis. This prevents intraoperative tumor embolization. A testicular prosthesis can be offered. Sperm banking should be discussed before surgery, as bilateral disease, adjuvant therapy, or contralateral testicular dysfunction may affect fertility.

For Stage I seminoma, three adjuvant strategies exist, and all yield survival rates approaching 99 to 100%:

1. Active surveillance is the preferred approach for patients who can comply with regular follow-up (physical exams, tumor markers, and imaging at defined intervals for 5+ years). Approximately 15 to 20% of Stage I seminoma patients will relapse, most within 2 years, but nearly all are salvaged with radiation or chemotherapy at the time of recurrence. The advantage is avoidance of treatment toxicity in the 80% who are already cured by orchiectomy alone.

2. Adjuvant radiation (para-aortic field, 20 Gy in 10 fractions) reduces relapse to approximately 3 to 4% but exposes the patient to long-term risks including secondary malignancies and cardiovascular disease. This was historically the standard, but its use has declined.

3. Single-dose carboplatin (AUC 7, one cycle) reduces relapse to approximately 5% and is a convenient alternative. Two cycles may be used in some protocols. This approach avoids radiation-related toxicity.

For Stage IIA and IIB (non-bulky retroperitoneal disease), radiation therapy remains highly effective because seminoma is exquisitely radiosensitive. The radiation field (the "dog-leg" field) covers the para-aortic and ipsilateral iliac lymph nodes. Doses are 30 Gy for Stage IIA and 36 Gy for Stage IIB. For Stage IIB, cisplatin-based chemotherapy (3 cycles of BEP or 4 cycles of EP) is an equally acceptable alternative, particularly when the nodal mass approaches the upper boundary of this stage.

For bulky Stage IIC and Stage III, chemotherapy is the standard. The BEP regimen consists of:

• Bleomycin 30 units IV, days 1, 8, and 15 of each cycle

• Etoposide 100 mg/m${}^2^2$ IV, days 1 through 5

• Cisplatin 20 mg/m${}^2^2$ IV, days 1 through 5

• Cycle length: 21 days

Good-prognosis patients receive 3 cycles of BEP. Intermediate-prognosis patients receive 4 cycles of BEP.

Bleomycin pulmonary toxicity is an important consideration. Risk factors include cumulative dose (>300 units total), age >40, renal impairment, and concurrent use of supplemental oxygen (relevant during anesthesia). Pulmonary function tests (DLCO) should be monitored during treatment. If bleomycin must be omitted, 4 cycles of EP (etoposide + cisplatin) is the substitute.

After chemotherapy for advanced seminoma, residual masses are managed differently than in NSGCT. If the residual mass is <3 cm, observation with serial imaging is recommended, as these are usually fibrosis or necrosis. If the residual mass is >3 cm, FDG-PET/CT is obtained at least 6 weeks post-chemotherapy. A PET-positive residual mass warrants surgical resection or salvage chemotherapy. A PET-negative mass is observed.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most tested pitfall on seminoma questions is the AFP rule. If a vignette describes a testicular mass with biopsy showing pure seminoma but includes an elevated serum AFP, the correct answer is to treat as a non-seminomatous germ cell tumor. Students who anchor on the histology and select "radiation therapy" will get the question wrong. The elevated AFP overrides the pathologic diagnosis because it signals the presence of yolk sac elements that were not captured in the biopsy specimen.

The second major trap involves the surgical approach. The correct procedure is radical inguinal orchiectomy. Answer choices that include "transscrotal biopsy" or "transscrotal orchiectomy" are deliberate distractors. The inguinal approach is mandatory to preserve normal scrotal lymphatic drainage and prevent tumor seeding.

Third, do not confuse seminoma with testicular lymphoma in older patients. When a vignette presents a man over 60 with a testicular mass (especially bilateral), lymphoma should be at the top of the differential. Seminoma peaks at 25 to 45, and a primary testicular tumor in an elderly patient is more likely to be lymphoma than a germ cell tumor.

Fourth, understand the role of radiation versus chemotherapy. Seminoma is radiosensitive; NSGCT is not. However, radiation is only appropriate for Stage I and non-bulky Stage II seminoma. For bulky disease (IIC) and metastatic disease (Stage III), chemotherapy with BEP is the standard. A question that gives you a patient with Stage IIC seminoma and offers "radiation therapy" as an answer choice is testing whether you know the limits of radiation.

Fifth, remember the post-chemotherapy residual mass management difference: in seminoma, you observe small residual masses and use PET/CT for larger ones (>3 cm). In NSGCT, you proceed to retroperitoneal lymph node dissection (RPLND) for any residual mass. Mixing up these two approaches is a common error.

The core competency being tested with seminoma questions is your ability to integrate clinical presentation, tumor markers, and histology into a single diagnostic and management algorithm, while recognizing the critical exceptions (AFP rule, surgical approach, age-based differentials) that distinguish a correct answer from a well-constructed distractor.