Seminoma’s Architectural Variants, Immunophenotype and Differential Diagnostic

Introduction: Although rare, representing only 1–2% of all tumours in man, testicular germ cell tumours (TGCT) are the overwhelming majority (98%) of testicular neoplasms among male patients between 15 to 40 years of age. Due to their increasing incidence and the characteristically young targeted population, they become a problem of public health in some developed countries. Classically, TGCTs are classified in three main groups: classical seminoma, non-seminomatous germ cell tumours (pure or mixed) and the spermatocytic seminoma. As SS is a very rare tumour, with a benign evolution, in practice the main differential diagnosis to be made is between seminoma and non-seminomatous tumours. Distinguishing these two categories is essential as the prognostic and the therapeutic approach is very different: if radiotherapy is the main treatment for seminoma, for non- seminomatous tumour a cisplatin based chemotherapy will be proposed.
Material and methods: This study proposes a morphologic and immunohistochemical evaluation of an important number of seminomas emphasising their unusual architectural features.
Results: The majority of the seminomas (46 cases), either pure or as a component of non-seminomatous germ cell tumours, had a solid architecture. We identified syncytiotrophoblasts cells in only one case in conventional stain and 11 cases were associated with a scattered intertubular spread. Eighteen cases showed unusual patterns: tubular-trabecular (9 cases), microcystic areas (5 cases) and 4 seminomas had focal nuclear pleomorphism. Areas of focal or extensive fibrosis and hemosiderin laden macrophages were identified in 4 cases. IGCNU, conventional seminomas and all the unusual architectural variants of seminoma had the same immunoprofile: positivity for PLAP and negativity for AFP and CD30.
Conclusions: Our study confirms the high architectural variability of seminomas, with unusual histological patterns like intertubular, tubular-trabecular, microcystic and pleomorphic. In the great majority of cases, the diagnosis of seminoma relies on the histological pattern in conventional stain. Only few cases may be prone to be diagnostically challenging, including tumours with unusual patterns. In these circumstances, the use of a panel of antibodies is mandatory for a correct diagnosis.