To the Editor: Dr Kim and colleagues1 found elevated serum osteopontin levels in patients
with ovarian carcinoma. While the authors' approach has high sensitivity,
the nonspecific nature of osteopontin expression in many diseases limits the
potential clinical application of serum osteopontin as a unique biomarker
for ovarian cancer.
Test specificity is central to any biomarker or screening program. Osteopontin
may be expressed in many inflammatory and noninflammatory diseases including
cancers of varied tissue origin.2,3
Although a variety of cell types express osteopontin, macrophages are a major
source.2 Even in carcinoma, there is evidence
that infiltrating macrophages rather than tumor cells are the principal source
of osteopontin.3 Prior investigations have
shown very high levels of osteopontin in hemodialysis patients with arterial
atherosclerosis and in patients with gram-negative sepsis.4
These studies suggest that assays of total serum osteopontin alone will lack
sufficient specificity to be a clinically applicable cancer biomarker.
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