Ontogeny histologic subtypes and pattern of spread

Ontogeny

Seminoma is a malignant tumor of seminiferous tubular epithelium. It is believed to represent a common precursor of other germ cell tumors [5], including all forms of nonseminomatous germ cell tumors (NSGCT). This common origin may have important implications for men because approximately 15% of men who have seminoma may relapse with NSGCT following definitive therapy. One recent CDNA expression profiling study among histologically pure seminoma identified two subgroups of seminoma. One was pure, whereas the other had molecular and immunophe-notypic features of embryonal cancer admixed with seminoma [6]. All seminomas are believed to have progressed from an in situ stage, known as intratubular germ cell neoplasia.

Histologic subtypes

Three histologic subtypes of seminoma are described: anaplastic, classic, and spermatocytic. Anaplastic seminoma demonstrates microscopic features of a more aggressive malignancy with enhanced mitosis, nuclear pleomorphism, and higher nuclear to cytoplasmic ratio. Although anaplastic seminomas present at higher stage, the stage for stage prognosis is equivalent to that of classic seminoma [5].

Spermatocytic seminoma is a unique human neoplasm. It accounts for 1% to 2% of cases and elderly men (over age 50) typically present with this disease [7]. The metastatic potential of sper-matocytic seminoma is minimal, although rare cases of sarcomatous dedifferentiation [8] and frank metastases from the seminoma itself have been reported [9]. Men who have spermatocytic seminoma generally do not require additional therapy post-orchidectomy. It is now well accepted that the nonspermatocytic forms of semi-noma and spermatocytic seminoma originate from different pathways. Spermatocytic semi-noma is currently believed to arise from a more mature [10] germ cell, such as a spermatogonium or spermatocyte, and have different patterns of DNA flow cytometry, genetic karyotyping, and comparative genomic hybridization [11] compared with classic and anaplastic seminomas.

Patterns of spread

Compared with NSGCT, seminoma has a favorable natural history and indolent growth pattern. It is estimated that 70% [12] of semino-mas present with clinical stage I disease. Semino-mas typically spread by way of the testicular lymphatics to the retroperitoneal lymph nodes. On the left side these are principally para-aortic and on the right side, interaortocaval. The second level of spread after the retroperitoneum is the mediastinal lymph nodes. Visceral spread to lung, liver, and other organs is uncommon.

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