Scrotum  

This case first appeared as Performance Improvement Program in Surgical Pathology (PIP) 2022, Case 17, and is a mixed germ cell tumor in the scrotum. The information provided in this case was accurate and correct at the time of publication in 2022.  Any changes in terminology since the time of publication may not be reflected in this case.  

The sections show a mixed neoplasm with focal necrosis. Scattered papillary structures are seen lined by columnar to cuboidal tumor cells with a high N:C ratio and scant clear to eosinophilic cytoplasm. Separate areas show sheets of primitive-appearing cells with higher nuclear atypia and prominent nucleoli. These features are consistent with a diagnosis of a recurrent mixed germ cell tumor (MGCT), with a combination of yolk sac tumor (YST), described first above, and embryonal carcinoma (EC), described second above, components.

Testicular neoplasms are divided into primary germ cell tumors (GCT), which account for 95% of cases of testicular cancer, and non-GCT, which account for fewer than 5% of cases. Testicular GCT typically occurs in patients aged 15 to 40. Risk factors include cryptorchidism, affected siblings, subfertility, testicular microlithiasis, testicular dysgenesis, Li-Fraumeni syndrome, and prior testicular GCT.  

Testicular GCT (TGCT) are divided into two major groups, based on whether they are derived from precursor germ cell neoplasia in situ (GCNIS). Non-GCNIS-derived TGCTs are mainly pre-pubertal, and GCNIS-derived TGCTs are mainly post-pubertal. Non-GCNIS-derived TGCTs show diploidy or aneuploidy with gain of chromosomes 1q, 12, and 20q, and loss of chromosomes 1p, 4, and 6p. GCNIS-derived TGCTs are associated with aneuploidy or triploidy; chromosome 12p amplification (often isochromosome 12p); gain of chromosomes X, 7, 8, 21; and loss of chromosomes Y, 1p, 11, 13, and 18. Molecular testing with i(12p) analysis is helpful to confirm TGCT origin in metastatic tumors, particularly those with somatic-type differentiation, and to differentiate between pre-pubertal and post-pubertal type teratomas.

Mixed germ cell tumor (MGCT) of the testis contains two or more GCT types. This is the second most common GCT in adults, following pure seminoma. It comprises 30% to 50% of cases, with an average age at diagnosis of 30 years. Presenting symptoms may include testicular pain, testicular enlargement, or metastasis. Serum AFP and hCG may be elevated, depending on the presence of YST elements and syncytiotrophoblastic cells, respectively. MGCT has a variegated appearance on cut surface, reflecting the various tissue components, with accompanying necrosis and hemorrhage. The more common combinations in a MGCT are EC with teratoma, seminoma, or yolk sac tumor. All components and their approximate percentages should be reported. The proportion of the EC component has important prognostic value in predicting metastatic disease in patients with clinical stage 1 disease.

Embryonal carcinoma (EC) is a malignant GCT composed of primitive epithelial tumor cells recapitulating early stages of embryonic development. It is a common component of MGCT (40%). Most patients present in their 20s to 30s with a testicular mass. AFP, hCG, and LDH levels may be elevated. There is frequent hemorrhage and tumor necrosis. The classic architectural patterns are solid, glandular, and papillary. The cytological features include cells with large overlapping vesicular nuclei, prominent nucleoli, amphophilic cytoplasm, and indistinct cell borders. Mitoses are numerous. EC is positive for CD30, OCT3/4, SALL4, PLAP, and focally AFP. EC is negative for CD117, glypican 3, and hCG.  

Yolk sac tumor (YST) is a malignant GCT and occurs in two age peaks. Pre-pubertal YST is the most common GCT in the pediatric population (mean age is 16 to 18 months) occurring in a pure form, is not associated with GCNIS, and is associated with a better prognosis. Post-pubertal YST occurs mainly in adults (25 to 35 years), is associated with GCNIS, and is usually admixed with other GCTs. Serum AFP is elevated in more than 95% of patients. Histologically, numerous architectural patterns are seen in varying proportions. Microcystic is the most common, while less common patterns include solid, myxomatous, papillary, glandular, macrocystic, alveolar, sarcomatoid, polyvesicular vitelline, hepatoid, and parietal. Intra- and extracellular PAS-positive hyaline globules may be seen. Tumor cells are epithelioid with clear or vacuolated pale eosinophilic cytoplasm, cuboidal, columnar, or spindled. Around 50% of YSTs contain Schiller–Duval bodies (papillary structures within cystic spaces, lined by cuboidal/columnar cells with a distinct central vessel). YST is positive for AFP, glypican 3, and SALL4. YST is negative for OCT3/4, CD30, CD117, and PLAP.

Seminoma is the most common testicular GCT, comprising > 50% of GCT, and presents in young adult patients (average age of 37 to 41 years) with painless testicular enlargement. Serum LDH and hCG may be elevated, while AFP is usually not increased. Tumor cells have a solid or nested growth pattern separated by thin fibrous septa rich in lymphocytes. Individual tumor cells are large, uniform, and round to polygonal with distinct cell membranes and lightly eosinophilic to clear cytoplasm due to the presence of glycogen, demonstrable by a periodic acid-Schiff (PAS) stain. The nuclei contain one or more prominent nucleoli. Syncytiotrophoblasts and granulomatous inflammation can occur. Mitoses are readily identifiable. Seminoma is positive for OCT3/4, CD117, D2-40, and PLAP. CD30, AFP, and glypican 3 are negative.

Choriocarcinoma (CC) is seen in approximately 8% of MGCT; pure CC is rare. CC occurs in young patients in the second and third decades of life, mostly presenting with metastatic symptoms due to hematogenous spread rather than a testicular mass. CC has a worse prognosis than other types of GCT due to its predilection for rapid hematogenous dissemination and a high incidence of brain metastasis. Serum hCG levels are markedly increased (more than 100,000 IU/L). It is composed of varying amounts of syncytiotrophoblasts (large multinucleated cells with eosinophilic cytoplasm), cytotrophoblasts (polygonal cells with single nuclei and prominent nucleoli), intermediate trophoblasts (cells larger than cytotrophoblasts, with clear cytoplasm, and single nuclei), and adjacent testicular parenchyma with GCNIS. Immunohistochemically, CC is positive for hCG and glypican 3, and negative for CD30, OCT3/4, and CD117.

Teratoma originates from germ cells with tissue derived from more than one embryonic germ layer (endoderm, ectoderm, mesoderm). Pre-pubertal type teratoma is the second most common GCT in children and occurs in a pure form. Post-pubertal type teratoma usually occurs as a component of MGCT, with a median age of presentation of 25 to 35 years and is associated with GCNIS and chromosome 12p amplification. Serum markers are usually normal. Histologically, teratoma shows varying tissue types such as squamous epithelium, glandular tissue, cartilage, or neuropil. Rarely, malignancies can arise within the tissue types, referred to as teratoma with somatic-type malignancy. Teratoma is negative for PLAP, OCT3/4, CD30, and SALL4. 

1. Which of the following is true regarding germ cell tumors? 
    
   1. Embryonal carcinoma is the most common component of mixed germ cell tumors.
   2. OCT3/4 can be used to differentiate seminoma from embryonal carcinoma.
   3. Pre-pubertal type teratomas are associated with germ cell neoplasia in situ.
   4. Serum tumor markers are usually elevated in testicular teratomas.
   5. Yolk sac tumors generally occur as part of a mixed germ cell tumor in children.  
       
2. Which of the following chromosomal abnormalities is most frequently seen in germ cell tumors derived from germ cell neoplasia in situ of the testis? 
    
   1. del(12p)  
   2. i(9p)
   3. i(12p)
   4. inv(9)
   5. t(11;18)   
       
3. A testicular tumor in a 25-year-old shows diffuse positivity for SALL4, with focal areas positive for CD117 and negative for CD30, and separate areas focally positive for CD30 and negative for CD117. What is the most likely diagnosis of this tumor? 
    
   1. Choriocarcinoma
   2. Embryonal carcinoma
   3. Mixed germ cell tumor, with seminoma and choriocarcinoma  
   4. Mixed germ cell tumor, with seminoma and embryonal carcinoma  
   5. Seminoma 

1. Al-Obaidy KI, Idrees MT. Testicular tumors: a contemporary update on morphologic, immunohistochemical and molecular features. Adv Anat Pathol. 2021;28(4):258-275.
2. Bahrami A, Ro JY, Ayala AG. An overview of testicular germ cell tumors. Arch Pathol Lab Med. 2007;131(8):1267-1280.
3. Kao C-S, Ulbright TM, Young RH, Idrees MT. Testicular embryonal carcinoma: a morphologic study of 180 cases highlighting unusual and unemphasized aspects. Am J Surg Pathol. 2014;38(5):689-697.
4. Looijenga LHJ, Van der Kwast TH, Grignon D, et al. Re: Report from the International Society of Urological Pathology (ISUP) consultation conference on molecular pathology of urogenital cancers: IV: current and future utilization of molecular-genetic tests for testicular germ cell tumors. Am J Surg Pathol. 2020; 44(7):e66-e79.
5. Rajpert-De Meyts E, McGlynn KA, Okamoto K, Jewett MAS, Bokemeyer C. Testicular germ cell tumours. Lancet. 2016;387(10029):1762-1774.
6. Wetherell D, Weerakoon M, Williams D, et al. Mature and immature teratoma: a review of pathological characteristics and treatment options. Med Surg Urol. 2014;03:124.

1. Embryonal carcinoma is the most common component of mixed germ cell tumors. (a)  
2. i(12p) (c)
3. Mixed germ cell tumor, with seminoma and embryonal carcinoma (d)