Validation of neurokinin a assays in the United States and Europe.

OBJECTIVES: International cooperative group trials require specific, sensitive biomarker assays that are validated between continents. Neurokinin A (NKA) has been shown to be a powerful independent predictor of a poor prognosis in well-differentiated midgut neuroendocrine tumors. We hypothesized that NKA concentrations of clinical specimens evaluated in NKA assays in the United States and the United Kingdom would be equivalent, even though assay techniques were significantly different. METHODS: Frozen clinical specimen aliquots were shipped from the United States to the United Kingdom (n = 67), and from United Kingdom to the United States (n = 50). In addition, spiked plasma standards and medium-spiked standards were exchanged. Samples from the United States were directly assayed in a radioimmunoassay, whereas the UK specimens were extracted, and the reconstituted specimens assayed in the radioimmunoassay. Neurokinin A values from the 2 studies were analyzed by regression analysis. RESULTS: The NKA values from the US and UK laboratories were essentially identical (United States to United Kingdom, r = 0.88, P < 0.0001; and United Kingdom to United States, r = 0.96, P < 0.0001). CONCLUSIONS: Validation of biomarker assays across continents will ensure that laboratory observations made by researchers are equivalent and that prediction of clinical outcomes based on these assays is also reliable.

Development of a highly sensitive and specific carboxy-terminal human pancreastatin assay to monitor neuroendocrine tumor behavior.

OBJECTIVE: Pancreastatin is a fragment of the chromogranin A (CgA) molecule. Existing pancreastatin assays, which depend on antibodies that cross-react in varying percents with the larger prohormone, may lack sensitivity and specificity to detect small changes in neuroendocrine tumor volume. METHODS: We developed a highly specific, sensitive pancreastatin assay. The antibody used recognizes the carboxyl terminal of the peptide hormone and was raised against a 17-amino acid porcine pancreastatin fragment with high homology with the carboxy-terminal amino acids 286-301 of the human CgA. RESULTS: Our assay measures more than 95% of circulating pancreastatin levels; has little or no cross-reactivity with CgA, even at plasma concentrations of 1000 ng/mL; and can detect pancreastatin levels of 17 pg/mL. Interassay reproducibility for the pancreastatin radioimmunoassay was determined from results of 3 quality control pools in 15 consecutive assays. Coefficients of variation for low, medium, and high pancreastatin levels were less than 20%. The sensitivity of serial pancreastatin assays to detect early liver tumor activity was demonstrated in 2 patients with slowly progressive neuroendocrine tumors and in patients undergoing surgical cytoreduction. CONCLUSIONS: This highly specific, sensitive pancreastatin assay can detect small changes in liver tumor progression and is up to 100-fold more sensitive and specific than CgA assays in the United States.