1. Introduction
Germ cell tumors (GCTs) are a family of neoplasms with diverse
histopathological, clinical features and prognosis, which are widely
considered to arise from almighty primordial germ
cells(1). Gonads are the most common organ that GCTs
predominantly occurs, while a small proportion of GCTs primarily
develops in extra-gonad regions such as pineal gland, coccyx,
mediastinum, retroperitoneum(2) and the anterior
mediastinum is the prior anatomical position in which approximately
10–20% of primary extra-gonad GCTs occur(3).
Pathologically, GCTs are divided into two categories: pure seminomas and
non-seminomatous germ cell tumors (NSGCT)(4).
Teratoma, a subtype of NSGCT, accounts for about 40% - 60% of all
mediastinal GCTs with the majority of its histology being
mature(5). While the immature teratoma, a particularly
rare subtype of teratomas with poor clinical prognosis, accounts for
only approximately 1.8% of mediastinal GCTs and about 4% of
mediastinal teratomas(3). Moreover, the immature
teratoma with somatic-type malignant transformation (SM) is extremely
rare(6), and there are only a few cases described
about this topic(7-12). We herein report a case of a
chemotherapy-resistant and extremely giant immature teratoma who
received en bloc resection with pathologic findings of foci of sarcoma
and poorly differentiated squamous cell carcinoma. To our best
knowledge, this is the largest primary mediastinum immature teratoma
with somatic-type malignant transformation treated with an en bloc
resection so far.