Testicular teratoma is a germ cell-derived neoplasia composed of different somatic tissues and can be derived from one or more germinal layers (endoderm, mesoderm, and ectoderm).
According to the WHO classification, germ cell tumors of the testis are divided into two main groups:
Germ cell neoplasms comprise germ cell neoplasia in situ (GCNIS), seminoma, and non-seminoma (NSGCT). The latter encompasses teratoma (postpubertal type), embryonal carcinoma, choriocarcinoma, yolk sac tumors (YSTs).
non-GCNIS tumors include spermatocytic tumors, YST prepubertal type, teratoma (prepubertal type).
The vast majority of adult testicular teratomas are malignant germ cell tumors. Teratoma accounts for about 3 to 7% of NSGCT and about 50% of mixed GCTs. As stated in the WHO classification (2016), two types of testicular teratomas exist:
Prepubertal teratoma is considered an indolent tumor and is not associated with germ cell neoplasia in situ; the testis shows normal spermatogenesis and has no metastatic potential. This histotype is not specific to children and can be found in adult patients. This group includes dermoid or epidermoid cysts.
Postpubertal teratoma is GCNIS-derived and has metastatic potential (metastasizes in 22% to 37% of cases).
A rare encounter is a teratoma with somatic-type transformation, defined as “teratoma that develops a distinct secondary component that resembles a somatic-type malignant neoplasm," which has specific prognosis and treatment and needs to be distinguished from postpubertal teratomas.
The outcomes for patients with localized disease are good, and they are candidates for surgical therapy. Patients with metastatic disease have a poorer outcome that depends on several clinical and pathological factors and are treated in a multimodal approach involving different medical professionals. Metastatic tumors do not respond well to chemotherapy, and the goal is to achieve a complete surgical resection.
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