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.