Complex sentence: Also, only about 50% of patients with early stage ovarian cancer have elevated CA-125 levels, meaning that CA-125 has particularly poor sensitivity for ovarian cancer before the onset of symptoms.
Split into simpler sentences: Also, only about 50% of patients with early stage ovarian cancer have elevated CA-125 levels. Since many patients with early stage ovarian cancer do not have elevated levels of CA-125, this biomarker has poor sensitivity for ovarian cancer, especially before the onset of symptoms.