Mitotic figures are usually abundant and the lymphocytic infiltrate and granulomas seen in classic seminoma are absent. Spermatocytic seminoma is an extremely indolent tumor with rather limited malignant potential and rarely if ever metastasizes. Grossly, the tumors are large, often hemorrhagic and necrotic producing a variegated cut surface. Tumor replaces the whole testis. Histologically, they are extremely pleomorphic and show a variety of patterns forming glands, tubules, and even primitive embryo-like structures.
Many mitotic figures are present.
Anaplastic and solid undifferentiated areas may present as sheets of cells with large, hyperchromatic nuclei, prominent nucleoli and poorly-defines cell borders. Poorly differentiated area in embryonal carcinoma. When large numbers of the embryo-like structures are present the tumor is referred to as a polyembryoma. These structures contain a disc and two cavities surrounded by loose mesenchyme simulating a 2 week embryo. Embryonal carcinoma metastasizes early and widely via both lymphatic and hematogenous routes.