Pitfalls in the interpretation of tumour markers

EDITOR,—We do not agree with H S Pandha and colleagues that poor sensitivity and specificity of assays cause a major problem in the measurement of (alpha) fetoprotein concentrations.1 Measurements of (alpha) fetoprotein are used in several clinical situations, including to diagnose and monitor neoplastic disorders (such as germ cell tumours and hepatomas) and in antenatal screening for Down's syndrome and neural tube defects. Modern immunoassays for (alpha) fetoprotein have adequate sensitivity, and it is important for clinical laboratories to use an assay that is specific for (alpha) fetoprotein but that adequately detects all its molecular forms in view of the variety of clinical settings in which (alpha) fetoprotein is measured. In specific cases, identification of the particular form of (alpha) fetoprotein secreted may be valuable, but this is not generally required.

Although concentrations of both (alpha) fetoprotein and human chorionic gonadotrophin were initially raised in the case reported, the authors do not comment on the absence of any increase in the concentration of human chorionic gonadotrophin concomitant with the second increase in (alpha) fetoprotein concentration. This might have suggested that this increase in (alpha) fetoprotein concentration was not due to recurrence of the primary tumour. However, recurrent tumour deposits or metastases may not secrete the same tumour markers (or may not secrete them in the same proportions) as the primary tumour, and this may cause particular difficulty with heterogeneous tumours such as teratomas.