Basic Classification
All testicular neoplasms are divided into two major groups:
- Germ Cell Tumors. Originate from primordial germ cells. They account for the vast majority (95%) of all testicular neoplasms. They are characterized by malignant behavior, a tendency for rapid dissemination, and extensive metastasis. They may have a single histologic type or a mixed composition.
- Non-Germ Cell Tumors. Develop from sex cord-stromal elements (Sertoli and Leydig cells). As a rule, they have a benign clinical course, less frequently exhibiting malignant potential. Some of these tumors are capable of producing steroid hormones, leading to specific symptoms (e.g., gynecomastia).
Germ Cell Tumors of a Single Histologic Type
This group includes several distinct nosologies with characteristic morphology:
- Classical Seminoma. A malignant tumor composed of monomorphic germ cells. Grossly, it is a well-circumscribed, lobulated, yellowish-pink nodule. Microscopically, cells form alveolar nests, and tumor growth is accompanied by a lymphocytic and granulomatous reaction. hCG is frequently elevated.
- Spermatocytic Tumor. A rare variant occurring in older adults. It consists of three cell types (lymphocyte-like, intermediate, large). It is characterized by slow, asymptomatic growth and extremely rare metastasis.
- Embryonal Carcinoma. An aggressive tumor of young adult males (associated with HLA-B13+). Grossly, it presents as a soft nodule with foci of necrosis and hemorrhage. Cells are pleomorphic with prominent nucleoli, forming solid and papillary structures. In one-third of cases, it expresses $\alpha$-fetoprotein (AFP).
- Yolk Sac Tumor. Most commonly affects children under 3 years of age. The main marker is a dramatic elevation of AFP in 100% of cases. Histology reveals reticular honeycomb structures and Schiller-Duval bodies. The prognosis in children is usually favorable.
- Choriocarcinoma. An extremely aggressive neoplasm with trophoblastic differentiation (cytotrophoblast and syncytiotrophoblast). It gives rise to early and widespread hematogenous metastases, while the primary nodule may undergo fibrosis and scarring.
- Teratoma. A tumor with differentiation into somatic-type tissues. It can be mature (containing normal tissue analogs, e.g., dermoid cyst) and immature (containing embryonic tissues, such as fetal glands or neuroepithelium).
Sex Cord-Stromal Tumors
Account for approximately 5% of all testicular neoplasms. They include tumors arising from supporting and interstitial cells:
- Leydig Cell Tumor (Leydigioma). Composed of polygonal cells whose cytoplasm often contains lipids, lipofuscin, and Reinke crystals. In 10% of cases, it exhibits malignant potential.
- Sertoli Cell Tumor (Sertolioma). A rare yellowish nodule. Microscopically, it may present in tubular, sclerosing, or large-cell calcifying variants.
- Granulosa Cell Tumors. Subdivided into the adult type (frequently accompanied by gynecomastia) and the juvenile type (the most common tumor in the first 6 months of life, associated with cryptorchidism).