Testicular Pathology — Germ Cell and Other Tumors

Germ Cell Tumor Development

Primordial Germ Cell Origin and Neoplastic Transformation

• GCTs originate from intratubular germ cell neoplasia, unclassified (IGCNU), also known as carcinoma in situ (CIS)
• IGCNU represents malignant transformation of primitive germ cells during fetal development or early postnatal life, with presentation typically delayed until adolescence or adulthood due to slow growth kinetics
• Malignant transformation involves loss of normal germ cell differentiation programs and acquisition of stem cell-like properties characterized by increased proliferation and survival signaling

Key Molecular Abnormalities

• Isochromosome 12 [i(12p)] present in 80% of GCTs; alternative gain of 12p material via other mechanisms in remaining cases—this is the most consistent genetic abnormality and represents pathognomonic marker for GCTs
• KIT mutations (40-60% of seminomas and some nonseminomatous tumors) activate tyrosine kinase signaling, promoting proliferation and survival
• TP53 mutations and RAS pathway alterations contribute to loss of apoptosis and cell cycle control
• Epigenetic modifications including aberrant DNA methylation patterns and loss of imprinted gene expression (H19, IGF2) facilitate malignant transformation

Histologic Differentiation Pathways

• Seminomatous tumors represent most differentiated form, morphologically resembling primordial germ cells with preserved epithelioid features
• Nonseminomatous tumors reflect varying degrees of differentiation along embryonic and extragonadal pathways:
• Embryonal carcinoma (EC): primitive undifferentiated component, morphologically resembles embryonic ectoderm
• Yolk sac tumor (YST): endodermal differentiation with distinctive microvesicular and papillary patterns
• Choriocarcinoma (CC): trophoblastic differentiation with syncytiotrophoblastic and cytotrophoblastic components
• Teratoma: mesodermal and endodermal differentiation with mature and/or immature tissue elements
• These components coexist in mixed GCTs and may undergo clonal evolution during treatment

Tumor Microenvironment and Immunobiology

• Seminomas demonstrate prominent lymphocytic infiltration with CD8+ T cells and Th1 polarization, contributing to chemotherapy sensitivity
• Dysregulated expression of pluripotency factors (OCT4, NANOG, SOX2) maintains stem cell phenotype and dedifferentiation capacity
• Activation of MAPK/ERK and PI3K/AKT pathways promotes survival independent of normal growth signals

Primary Risk Factors

Cryptorchidism (Undescended Testis)

• Single most important risk factor, increasing relative risk 4-8 fold regardless of orchiopexy timing
• Malignant potential exists in both the cryptorchid testis and the contralateral normally descended testis, suggesting systemic germ cell dysgenesis
• Risk persists even after late orchiopexy, indicating that cryptorchidism reflects underlying gonadal dysgenesis rather than causative thermal/mechanical factors alone
• Intra-abdominal location confers higher risk than inguinal location

Gonadal Dysgenesis and Intersex Conditions

• Androgen insensitivity syndrome (AIS), both complete and partial forms, increase GCT risk substantially
• Gonadal dysgenesis including XY dysgenesis and Klinefelter syndrome (47,XXY) demonstrate 20-50 fold increased risk
• Hermaphroditism and pseudohermaphroditism represent significant risk factors
• IGCNU (CIS) found in 80% of dysgenetic gonads, representing precursor lesion

History of GCT

• Patients with prior GCT in one testis have 5-10% lifetime risk of contralateral GCT development
• Risk reflects systemic susceptibility to malignant transformation rather than direct tumor spread

Familial and Genetic Predisposition

• Familial clustering identified in 2-3% of GCT cases with 8-10 fold increased relative risk for relatives
• Inheritance pattern suggests autosomal dominant or X-linked dominant predisposition with incomplete penetrance
• Specific gene mutations remain largely unidentified, though candidate genes include BAC, DMRT1, KITLG
• Ethnicity: Caucasian populations demonstrate 5-10 fold higher incidence than African and Asian populations

Reproductive and Developmental Abnormalities

• Infertility and oligospermia associated with increased GCT risk, possibly reflecting shared gonadal dysgenesis
• Maternal estrogen exposure in utero (maternal diethylstilbestrol use) correlates with increased seminoma risk
• Low birth weight and prematurity represent minor risk factors

Other Risk Factors

• HIV infection associated with increased GCT incidence, though clinical significance debated
• Previous mediastinal or anterior neuraxis irradiation for lymphomas or other malignancies
• Tobacco use weakly associated with GCT risk

Non-germ Cell Tumors Risk Factors

Sex Cord-Stromal Tumors

• Leydig cell tumors: no well-established risk factors; may present in childhood or adulthood
• Sertoli cell tumors: association with Peutz-Jeghers syndrome (STK11 mutations) in juvenile form
• Granulosa cell tumors: rare, arise from juvenile or adult variants

Seminomatous Tumors (40% of GCTs)

Cardinal Symptoms

• Testicular mass/enlargement: hard, painless testicular swelling noted on self-examination or incidental physical exam in 90% of cases; mass typically unilateral but bilateral IGCNU present in 5%
• Testicular pain or ache: present in 10-15% at diagnosis, may represent hemorrhage into tumor or intra-testicular necrosis
• Palpable testicular heaviness: described by patients as sensation of weight or fullness in affected hemiscrotum

Physical Examination Findings

• Firm, enlarged testis (typically >2 cm) with loss of normal testicular consistency and texture
• Loss of testicular transillumination in presence of intratesticular mass (normal testis transilluminates)
• Absence of epididymal involvement or spermatic cord thickening in pure testicular tumor (distinguishes from epididymitis)
• Gynecomastia (15-20% of patients): reflects estrogen production from tumor or peripheral aromatization of testosterone; indicates systemic disease and hormonally active tumor burden

Constitutional and Systemic Symptoms

• Low back pain or abdominal pain: indicates retroperitoneal lymph node metastases
• Chest pain or respiratory symptoms: suggests mediastinal or pulmonary involvement
• Neurological symptoms: rare, indicates CNS metastases
• Weight loss, fatigue: nonspecific markers of advanced disease

Laboratory Findings

• Elevated serum α-fetoprotein (AFP): NOT elevated in pure seminoma (elevation suggests nonseminomatous element and reclassifies as nonseminomatous)
• Elevated human chorionic gonadotropin (hCG): present in 15-20% of pure seminomas; reflects syncytiotrophoblastic differentiation
• Elevated lactate dehydrogenase (LDH): present in 80% of advanced seminomas; correlates with tumor burden; most sensitive but least specific tumor marker
• Normal or mildly elevated testosterone: testicular tumors typically do not produce hormones (exception: Leydig cell tumors)

Imaging Correlates

• Ultrasound: hypoechoic or heterogeneous intratesticular mass with preserved testicular boundaries; color Doppler shows abnormal vascularity (increased flow)
• CT abdomen/pelvis: retroperitoneal lymphadenopathy in 15-25% of clinical stage I disease; retrocrural, interaortocaval, and pelvic node involvement most common

Nonseminomatous Germ Cell Tumors (60% of GCTs)

Cardinal Symptoms (Similar to Seminoma)

• Testicular mass: identical presentation to seminoma; firm, painless enlargement
• Testicular pain: more common in nonseminomatous tumors (20%) due to increased tendency toward hemorrhage and necrosis
• Gynecologic symptoms: less common than seminoma unless significant hCG production from trophoblastic elements

Specific Features by Histologic Subtype

Embryonal Carcinoma

• Most aggressive nonseminomatous element; frequently presents as hemorrhagic, necrotic mass
• Early lymph node and hematogenous metastases common (40% with metastases at presentation)
• Elevated AFP and/or hCG in majority of cases

Yolk Sac Tumor (Endodermal Sinus Tumor)

• Pediatric variant (90% of prepubertal testicular tumors) presents before age 5 years
• Adult variant associated with nonseminomatous mixed GCTs
• Markedly elevated AFP (often >1000 ng/mL)
• Pediatric form shows excellent prognosis with chemotherapy, in contrast to adult variants

Choriocarcinoma

• Severe gynecologic symptoms: marked nausea, vomiting, weight loss reflect high hormone production
• Profound gynecomastia and feminization: due to markedly elevated hCG (often >100,000 mIU/mL)
• Rapid progression with early hematogenous metastases to lungs, liver, brain
• Hemorrhagic metastases: distinctive hemorrhagic lung lesions reflect trophoblastic invasiveness

Teratoma (Adult)

• Mature teratoma elements may produce cystic masses with fluid-fluid levels on imaging
• Immature teratoma elements associated with systemic metastases and poor prognosis
• Tumor markers variable depending on admixed components (EC, YST elements produce markers)

Physical Examination — Sex Cord-Stromal Tumors

Leydig Cell Tumor

• Painless testicular mass, typically smaller than GCTs (usually <2 cm)
• Gynecomastia and sexual dysfunction: due to estrogen production or aromatization of excess testosterone
• Precocious puberty in children: presents with early pubic hair, penile enlargement, accelerated growth velocity
• Hypertension: occasional finding

Sertoli Cell Tumor

• Painless testicular mass, typically small
• Androgen or estrogen production if hormonally active; many are hormonally silent
• Gynecomastia variable; less common than with Leydig cell tumors
• Association with Peutz-Jeghers syndrome: facial lentiginosis and mucosal pigmentation

Presentation by Disease Stage

Clinical Stage I (No Radiographic Evidence of Metastases)

• 75% of all GCTs present in stage I
• Confined to testis on imaging; lymph nodes and distant organs negative
• Occult microscopic metastases present in 10-15% of clinical stage I nonseminomatous GCTs

Clinical Stage II (Regional Lymph Node Involvement)

• Retroperitoneal lymphadenopathy on imaging
• IIa: nodes <2 cm; IIb: nodes 2-5 cm; IIc: nodes >5 cm
• Back pain or abdominal pain may be initial presenting symptom

Clinical Stage III (Distant Metastases)

• Pulmonary (75-80%), hepatic (15%), CNS (3-5%), osseous (2-3%) involvement
• Constitutional symptoms more prominent

Histological Findings — Germ Cell Tumors

Seminoma (Classical/Typical Seminoma — Most Common)

• Uniform sheets of large polygonal cells with distinct cell membranes, clear cytoplasm ("glycogen-rich"), round nuclei with coarse chromatin
• Cells morphologically resemble primordial germ cells; nuclei demonstrate finely dispersed ("open") chromatin pattern distinct from lymphoid cells
• Granulomatous reaction with admixed lymphocytes, plasma cells, and epithelioid histiocytes creating distinctive stromal backdrop
• Mitotic figures prominent, reflecting high proliferative rate
• Fibrous septa dividing tumor into nodular compartments; rete testis may show extension
• Immunohistochemistry: OCT4+, CD117+, c-KIT+, SALL4+, D2-40+ (membrane and cytoplasm); PLAP+ (placental alkaline phosphatase); AFP-, hCG- (negative rules out nonseminomatous element)
• No syncytiotrophoblastic giant cells (if present, indicates nonseminomatous component—choriocarcinoma)

Spermatocytic Seminoma (Variant — Rare, Age >50 years)

• Three cell populations: small cells (microcytes) with condensed chromatin, intermediate cells, and large cells with prominent nucleoli ("filaria-like")
• Lacks prominent lymphocytic infiltration (contrast: classical seminoma has prominent lymphocytes)
• Occurs in older men (peak age 50-60 years); excellent prognosis with rare metastatic potential
• Immunohistochemistry: OCT4-, SALL4- (distinguishes from classical seminoma); D2-40-
• MGCT component rare (contrast: classical seminoma associated with IGCNU)

Embryonal Carcinoma (Undifferentiated Nonseminomatous Element)

• Sheets, glands, or cords of primitive undifferentiated epithelium with high nuclear-to-cytoplasmic ratio
• Nuclei vesicular with prominent nucleoli; numerous mitotic figures and apoptotic bodies
• Cytoplasm scant, basophilic; cells lack cohesion and show infiltrative borders
• Glandular structures may form with comedo-type necrosis within lumens
• Hemorrhage and necrosis prominent
• Immunohistochemistry: OCT4+, NANOG+, SOX2+ (pluripotency markers), SALL4+; CD30+; PLAP+, CK8+, EMA+; AFP variable (may be positive if YST differentiation present); hCG- (unless syncytiotrophoblastic cells present)
• Morphologic overlap with adenocarcinomas requires immunohistochemistry for definitive classification

Yolk Sac Tumor (Endodermal Sinus Tumor)

• Distinctive microcystic pattern: small cysts lined by primitive cuboidal epithelium with empty "space-filling" appearance
• Papillary structures with hyalinized cores (Schiller-Duval bodies): diagnostic hallmark consisting of central vessel within papillary frond lined by cuboidal epithelium
• Endodermal tubules and glands: varying degrees of differentiation from primitive to more organized structures
• Hyaline globules: periodic acid-Schiff (PAS) positive, diastase-resistant hyaline material within cytoplasm and stroma (corresponds to yolk sac proteins)
• Reticular and solid areas with admixed cell types
• Pediatric type (age <5 years): more myxoid stroma, less cellular, better differentiated
• Adult type (usually component of mixed GCT): **more cellular, pleomorphic nuclei, greater mitotic activity

Before any therapy

• Serum markers and imaging first: AFP, hCG, LDH drawn before orchiectomy and repeated after, since post-orchiectomy marker decline (following each analyte's half-life — AFP ~5-7 days, hCG ~1-3 days) drives staging and risk assignment under the IGCCCG system used by NCCN.
• Sperm banking: offered before orchiectomy, chemotherapy, or retroperitoneal surgery (NCCN Testicular Cancer guideline), because cisplatin-based regimens and retrograde ejaculation after node dissection both impair fertility.
• Emergencies first: bulky choriocarcinoma with pulmonary hemorrhage/respiratory failure, hemorrhagic brain metastasis, or hCG-mediated thyrotoxicosis requires stabilization and urgent oncology involvement before elective surgery.

Definitive local therapy

• Radical inguinal orchiectomy with high spermatic cord ligation: both diagnostic and therapeutic; the standard initial step for essentially every solid intratesticular mass (AUA/NCCN).
• Transscrotal biopsy or scrotal orchiectomy is contraindicated — it violates the scrotal lymphatics and seeds inguinal nodes, altering the drainage pattern that otherwise runs to the retroperitoneum.

Adjuvant/systemic therapy by histology

• Stage I seminoma: active surveillance is preferred (NCCN); alternatives are single-agent carboplatin or para-aortic radiotherapy, exploiting seminoma's exquisite radiosensitivity.
• Stage I nonseminoma: surveillance, nerve-sparing retroperitoneal lymph node dissection (RPLND), or one cycle of chemotherapy; lymphovascular invasion and embryonal predominance push toward active treatment.
• Advanced/metastatic disease: platinum-based combination chemotherapy — BEP (bleomycin, etoposide, cisplatin), or EP when bleomycin is undesirable (pre-existing lung disease, renal impairment, older patients).

Escalation and residual disease

• Salvage chemotherapy (e.g., paclitaxel/ifosfamide/cisplatin) or high-dose chemotherapy with autologous stem cell rescue for relapse.
• Post-chemotherapy residual mass in nonseminoma → surgical resection/RPLND, because teratoma is chemoresistant and radioresistant and may harbor viable carcinoma.
• Residual seminoma mass: FDG-PET after an interval guides observation versus resection.

Disease-related

• Hemorrhagic metastasis from choriocarcinoma — trophoblast invades vessels directly, producing bleeding brain and lung lesions; sudden headache, focal deficit, or hemoptysis is an emergency.
• hCG-induced hyperthyroidism: the alpha subunit of hCG cross-reacts with the TSH receptor; massive hCG elevation causes tachycardia, tremor, suppressed TSH — thyroid storm risk is an emergency.
• Ureteral obstruction/hydronephrosis and back pain from bulky retroperitoneal nodes; rising creatinine signals it.
• Choriocarcinoma syndrome: rapid tumor lysis or hemorrhage after starting chemotherapy in high-volume disease → hypoxemic respiratory failure; emergency.
• Tumor lysis syndrome: hyperkalemia, hyperuricemia, hyperphosphatemia, acute kidney injury shortly after cytoreduction; emergency.
• Contralateral tumor and infertility reflecting the underlying germ cell dysgenesis already present at diagnosis.

Treatment-related

• Bleomycin pulmonary toxicity: free-radical–mediated alveolar injury; nonproductive cough, exertional dyspnea, basilar crackles, and a falling DLCO — the earliest objective signal. High FiO₂ exposure (including perioperative) can precipitate deterioration.
• Cisplatin toxicities: nephrotoxicity (proximal tubular injury, magnesium wasting), ototoxicity (irreversible high-frequency hearing loss, tinnitus from hair cell damage), peripheral sensory neuropathy, and Raynaud phenomenon.
• Etoposide: topoisomerase II inhibition predisposes to secondary acute myeloid leukemia with KMT2A (MLL) 11q23 translocations, typically with short latency.
• Febrile neutropenia during chemotherapy — emergency; requires immediate empiric broad-spectrum antibiotics.
• Retrograde ejaculation after RPLND: injury to postganglionic sympathetic fibers/hypogastric plexus; absent antegrade ejaculate with sperm in post-orgasm urine. Nerve-sparing technique mitigates this.
• Growing teratoma syndrome: enlarging mass with normalizing markers during chemotherapy — surgery, not more chemotherapy.
• Late effects: hypogonadism, metabolic syndrome, cardiovascular disease, and radiation-associated second solid malignancies.

• Firm, painless, non-transilluminating intratesticular mass in a young man: the single best next step is scrotal ultrasound with Doppler, followed by serum AFP/hCG/LDH, then radical inguinal orchiectomy. The classic distractor is transscrotal biopsy — always wrong; it seeds inguinal nodes.
• Pure seminoma never elevates AFP. If AFP is elevated, the tumor is managed as a nonseminoma regardless of what the slide shows. hCG may be mildly elevated in seminoma from syncytiotrophoblasts.
• Schiller-Duval bodies (glomeruloid papillae with a central vessel) and PAS-positive hyaline globules = yolk sac tumor, the most common testicular tumor of boys under age 5, with markedly elevated AFP.
• Isochromosome 12p is the genetic signature of germ cell tumors, including extragonadal (mediastinal) primaries.
• Choriocarcinoma: very high hCG → gynecomastia, hyperthyroidism, and early hematogenous hemorrhagic metastases; the testicular primary may be small or regressed while metastases are bulky.
• Teratoma in a post-pubertal male is malignant and chemoresistant/radioresistant; a residual post-chemotherapy retroperitoneal mass with normal markers is resected surgically. Prepubertal mature teratoma is benign — a favorite trap.
• Seminoma is both radiosensitive and platinum-sensitive; lymphocytic infiltrate with fried-egg clear cells and fibrous septa is the buzzword pairing.
• Sex cord–stromal clues: Reinke crystals = Leydig cell tumor (precocious puberty in boys, gynecomastia in men); Sertoli cell tumor associates with Peutz-Jeghers syndrome.
• Age flips the diagnosis: a bilateral testicular mass in a man over 60 is more likely lymphoma than a germ cell tumor — the most common distractor in older-patient stems.