Testicular Tumours : Seminoma:

Seminoma:
Seminoma accounts for 50% of all testicular germ cell tumours.
It is the most likely germ cell tumour to present with a single histologic pattern.
Peak incidence is seen in the thirties.
Grossly, seminoma presents as a homogeneous, lobulated, gray-white mass, generally devoid of hemorrhage and necrosis. Tunica albuginea usually remains intact.
Microscopically, the mass is composed of large polyhedral seminoma cells with well-defined borders and abundant clear cytoplasm, large nuclei and prominent nucleoli.
Cytoplasmic glycogen is typically present.
The cells are arranged in solid sheets and may show a tendency to form tubular, papillary or glandular structures.
A fibrous stroma of variable density divides the tumor cells into irregular lobules; an accompanying lymphocytic infiltrate (usually T-cells) is present in most cases , granulomas may also be present. Neoplastic giant cells and syncytial cells, resembling placental syncytiotrophoblast may be seen in some cases.
Histochemically, Human chorionic gonadotropin (HCG) is present in such cells and presumably accounts for the elevated serum HCG levels detected in some patients with pure seminoma. The tumour cells contain placental alkaline phosphatase.
Classical seminoma cells do not contain alpha-fetoprotein (AFP).
Histologically, identical tumors may occur in the ovary (dysgerminomas) and central nervous system (germinoma).

Abstract: Seminoma with tubular, microcystic, and related patterns: a study of 28 cases of unusual morphologic variants that often cause confusion with yolk sac tumor. Am J Surg Pathol. 2005;29(4):500-5.
We report 28 testicular seminomas with cystic spaces of variable nature, sometimes accompanied by solid and hollow tubular patterns (12 cases). The spaces often suggested reticular or microcystic patterns of yolk sac tumor, and the solid and hollow tubular patterns often added to the diagnostic confusion. The tumors occurred in men 21 to 55 years old and on gross examination had the typical appearance of seminoma. On microscopic examination, the spaces ranged from small, closely packed and relatively regular to dilated, more dispersed and somewhat irregular. The hollow tubules appeared to result from central discohesion within nests of tumor. The spaces, particularly when large, often contained occasional tumor cells or inflammatory cells within pale edema fluid. The cytologic appearance of the cells lining the spaces, and in the surrounding tumor, retained the typical features of seminoma cells. Thirteen tumors (46%) either lacked (8 cases) or had very scant (5 cases) lymphocytes in the cystic and tubular areas, and hyaline globules were absent. Thirteen of 13 tumors were immunopositive for OCT-3/4 in the nontypical and typical areas; 9 of 10 were placental alkaline phosphatase positive, and 7 of 10 were c-Kit (CD117) positive. The same 13 cases were negative with cytokeratin (AE1/AE3) and alpha-fetoprotein stains. Distinction from yolk sac tumor is aided by the observation that the spaces of yolk sac tumor are often more irregular in their individual shapes and frequently form anastomosing channels. Additionally, the spaces of yolk sac tumor randomly merge with various other yolk sac tumor patterns. The cells lining spaces in yolk sac tumor are often flattened with compressed nuclei and lack the typical prominent nucleoli of seminoma cells. Paucity of lymphocytes and intracystic edema, however, are not differentially helpful, although basophilic fluid favors yolk sac tumor. A panel of immunostains (AE1/AE3, OCT-3/4, and alpha-fetoprotein) is helpful in the differential with yolk sac tumor in especially problematic cases. The edema and paucity of lymphocytes may suggest spermatocytic seminoma, but the varied cell types of that neoplasm are absent.

Abstract: Testicular seminoma: a clinicopathologic and immunohistochemical study of 105 cases with special reference to seminomas with atypical features. Int J Surg Pathol. 2002 Jan;10(1):23-32.
In spite of the high curability rates, rare cases of testicular seminoma behave in an unexpectedly aggressive manner. No effective markers are currently available that can predict such uncommon behavior. We studied 105 cases of testicular seminoma on whom the primary resection was performed at the Memorial Sloan-Kettering Cancer Center, New York, to investigate any relationship between morphology, immunohistochemical features, and clinical/pathological stages. Fifty-nine percent of the cases presented with pT stage 1 and 74 percent with American Joint Committee on Cancer (AJCC) stage I. In univariate analysis, tumor size, mitotic count, and presence of necrosis showed significant associations with pT stage (p = 0.0001, 0.0001, and 0.04, respectively), and the presence of vascular invasion (p = 0.0001, 0.0001, and 0.02, respectively). In multivariate analysis, both the tumor size and mitotic counts were independent predictors of pT stage (p = 0.0004 and 0.0001) and vascular invasion (p = 0.0004 and 0.0001). When tumors were separated on the basis of architectural and/or cytological atypia into "usual seminomas" and "seminomas with atypia", these were significantly associated with AJCC stage (p = 0.02), and c-kit protein (p = 0.0005) and CD30 expression (p = 0.02). In addition, "seminomas with atypia" also tended to show a higher proliferation activity as judged by Ki67 reactivity (p = 0.06), as well as express the marker of epithelial differentiation, Cam 5.2 (p = 0.09). In summary, we find that the morphologic features in testicular seminomas are associated with factors of clinical relevance. Also, "seminomas with atypia" differ from "usual seminomas" morphologically, present at a higher AJCC stage, and possibly represent an early step in transformation of seminomas toward a more aggressive phenotype. While not proposing a new entity, we suggest that when these atypical features are encountered in an otherwise classical seminoma, investigations must be performed to exclude an early carcinomatous differentiation or even earlier changes toward such a differentiation, such as lack of c-kit protein expression.