Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

II. Serum Tumor Markers
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also been identified in dogs with Sertoli cell tumors, making
it a potentially useful marker for identifying testicular
tumors ( Grootenhuis et al. , 1990 ).
2 . Serum Parathyroid Hormone
Increased serum parathyroid hormone (PTH) in the presence
of hypercalcemia has been considered sufficient for the
diagnosis of primary hyperparathyroidism. However, a retrospective
case-control study suggests that normal PTH concentrations
in the presence of hypercalcemia are an inappropriate
physiological response by the parathyroid gland and are also
consistent with primary hyperparathyroidism ( Feldman et al. ,
2005 ). Although primary hyperparathyroidism is an uncommon
disease of dogs and cats, both adenomas and carcinomas
of the parathyroid glands are reported in the literature and
should be considered among the differential diagnoses.
3 . Parathyroid Hormone-Related Protein
Hypercalcemia of malignancy is a well-recognized paraneoplastic
syndrome in animals. Hypercalcemia of malignancy
may arise from local bone resorption stimulated by
metastatic bone lesions or through endocrine factors that
disrupt normal calcium homeostasis ( Clines and Guise,
2005 ). Ectopic production of PTH by tumors is a rare
phenomenon, and most humoral hypercalcemia of malignancy
may be explained by the inappropriate production of
parathyroid hormone-related protein (PTHrP) by a variety
of tumors. Canine PTHrP is similar in structure and function
to PTH ( Rosol et al. , 1995 ). In dogs, PTHrP has been
implicated in hypercalcemia associated with apocrine gland
adenocarcinoma of the anal sac and lymphoma ( Rosol
et al. , 1992 ), melanoma ( Pressler et al. , 2002 ), thymoma
( Foley et al. , 2000 ), and poorly differentiated carcinoma.
Increased serum PTHrP concentration has been identified
in a small number of cats with humoral hypercalcemia of
malignancy associated with a variety of carcinomas and
lymphoma ( Bolliger et al. , 2002 ). Increased serum PTHrP
has also been described in a horse with hypercalcemia and
multiple myeloma ( Barton et al. , 2004 ).
4 . Thyroxine/Thyroglobulin
Estimates of the proportion of dogs with thyroid masses
that are revealed to be carcinoma range from 51% to 100%
( Scarlett, 1994 ). It is reported that 70% of dogs with thyroid
carcinomas have increased concentrations of serum
thyroglobulin, although these findings were not strongly
correlated with serum thyroxine (T 4 ) concentrations
(Verschueren et al. , 1991 ). It is generally accepted that most
dogs with thyroid carcinomas are euthyroid, but the contemporary
peer-reviewed literature is sparse with respect to
the prevalence of functional thyroid tumors in dogs.
In cats elevated serum total or free T 4 is generally
diagnostic for hyperthyroidism, although some cats with
nonthyroidal disease may have elevated free T 4 ( Peterson
et al. , 2001 ). Cats with equivocal results may require additional
evaluation with the triiodothyronine (T 3 ) suppression
test to confirm the diagnosis of hyperthyroidism ( Graves
and Peterson, 1994 ). Unlike dogs, most cats with hyperthyroidism
have a functional adenoma or adenomatous
hyperplasia rather than an underlying thyroid carcinoma.
Serial T 4 determinations are useful to monitor response to
therapy and detect a relapse following radioiodine treatment
( Peterson and Becker, 1995 ).
5 . Adrenocorticotropin Hormone/Cortisol
Hyperfunctioning adrenocortical tumors can be diagnosed by
measuring basal plasma cortisol concentration or changes in
plasma cortisol concentration from a variety of provocative
tests using natural or synthetic adrenocorticotropin hormone
(ACTH) stimulation or dexamethasone suppression. The
measurement of endogenous ACTH may help distinguish
primary adrenal disorders from those secondary to pituitary
gland dysfunction. The ratio of the precursor hormones
pro-opiomelanocortin and proadrenocorticotropin has been
recently correlated to the size of pituitary tumors in dogs with
hyperadrenocorticism ( Granger et al. , 2005 ). Measurement of
basal ACTH and the use of provocative testing with ACTH
have been reported for the diagnosis of equine pituitary pars
intermedia adenomas ( van der Kolk et al. , 1995 ).
6 . Sex Steroid Hormones
Measurement of plasma sex steroid hormones is useful for
characterization of equine GTCT in mares with clinical
signs attributable to high plasma concentrations of testosterone
or estrogen ( Meinecke and Gips, 1987 ; Stabenfeldt
et al. , 1979 ). Occasionally plasma progestins are elevated.
Considerable variation in sex steroid hormone profiles
exists among affected horses and may be due to the presence
of abnormal ovarian follicles, defects in aromatase
activity, or possible feedback inhibition affecting gonadotropin
secretion ( Hoque et al. , 2003 ).
Determination of plasma concentrations of androstenedione,
17-hydroxyprogesterone, and estradiol may be useful
in diagnosing adrenocortical neoplasia in ferrets ( Rosenthal
and Peterson, 1996 ). Likewise, increased plasma concentrations
of these adrenal sex hormones have been observed in
dogs with adrenal gland adenocarcinoma with provocative
testing using ACTH ( Hill et al. , 2005 ). Elevated plasma
progesterone has been described in a cat with a welldifferentiated
adrenocortical adenocarcinoma ( Boord and
Griffin, 1999 ).
Much literature exists surrounding the presence of estrogen
and progesterone receptors in mammary gland tumors
of the dog. Recent findings reveal that dogs with biologically
aggressive inflammatory mammary carcinomas had
increased serum and tissue concentrations of androgens