INTRODUCTION
Germinomas are the most common type of tumor among intracranial germ cell tumors, which predominantly affect children and young adults and respond well to chemotherapy and radiotherapy. Human chorionic gonadotropin (hCG) and alpha-fetoprotein (AFP) in the serum and cerebrospinal fluid (CSF) are helpful for the diagnosis of intracranial germ cell tumors.1 -4 Brain tumors producing hCG or AFP are mostly diagnosed as germ cell tumors, especially when the tumors arise in the pineal and neurohypophyseal regions. Notably, hCG is a glycoprotein composed of α and β subunits, synthesized by the syncytiotrophoblasts during pregnancy to maintain the corpus luteum. It is also produced by germ cell tumors such as germinomas, seminomas, and choriocarcinomas.5 The α subunit of hCG is a common protein in luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). In contrast, the β subunit is structurally specific to hCG.6 Therefore, hCG-related markers are measured using the β subunit for the diagnosis of intracranial germ cell tumors.7 In the past, germinomas that produce hCG were considered rare and described as “hCG-producing germinomas.”8 Recently, however, it has been shown that almost all germinomas produce some amount of hCG,9 and thus, its evaluation is vital for the diagnosis of germinoma. The differentiation between germinomas and choriocarcinomas are based on the histological findings and hCG levels; extreme elevations of hCG are indicative of choriocarcinoma. Furthermore, the measurement of hCG is also useful in the follow-up of germinomas and choriocarcinomas after treatment, because hCG is usually elevated before recurrence is detected with magnetic resonance imaging.10
There is some confusion with hCG measurements due to various hCG measuring kits available. Currently, there are three types of hCG-related markers used in clinical settings: hCGβ, intact hCG, and total hCG. Specifically, hCGβ is free hCGβ subunit that exists free from α subunits. Intact hCG is a combined form of the α and β subunit. Total hCG is the sum of hCGβ and intact hCG. Each medical institute adopts one or two of those hCG-related markers for serum/CSF samples, and the cutoff levels of the markers are different according to the manufacturers.
hCGβ may be a better tumor marker for germ cell tumors than intact hCG because of its specificity. However, the methods for measuring hCGs have not yet been standardized. We measured the values of the three hCG-related markers and evaluated them to clarify which marker is appropriate for the diagnosis of intracranial germinomas.