Serum levels of tumor markers and presence of human antimouse antibodies: implications for diagnosis and treatment with radiolabeled monoclonal antibodies.

Our study is based on 100 radioimmunodetections and five immunotherapies in 84 patients with advanced carcinomas. We used a monoclonal anti-CEA F(ab')2 and anti-CA 19.9 F(ab')2 antibody "cocktail" in 75% of the cases and monoclonal anti-alpha FP, anti-beta HCG, and OC 125 F(ab')2 antibodies in the other cases. In all cases, we determined plasma tumor marker levels immediately before imaging. The positivity of the scans was analyzed in relation to the levels of plasma markers. We found that the imaging should be planned only in the cases in which marker levels exceed minimum thresholds. We developed an enzymoimmunologic assay to measure antimouse antibodies. We found that patients who received monoclonal antibodies developed in the mouse produce such antimouse antibodies. The kinetics of this production are analyzed to define the optimal sequence for more than one administration of monoclonal antibodies.

Pitfalls and solutions in neuroblastoma diagnosis using radioiodine MIBG: our experience about 50 cases.

We have been among the first authors to point out that false negative cases could be observed with 131I-MIBG scintigraphy for neuroblastoma. We have observed until now ten of such false negative cases, 7 with primary tumor and 3 with bone metastases. Fifty 131I-MIBG scans were performed in 35 children with histologically proven neuroblastoma (24 grade IV) and compared to bone scans, CT and NMR images, ultrasound and clinical results. The visualization of the primary tumor shows a higher sensitivity with MIBG (79%) than with bone scans (47%) and a 100% specificity with each method. MIBG and bone scans, for bone metastases, are similar in the sensitivity (87.5%) but MIBG is much more specific (100%) than bone scan (81%). These results clearly confirm the superiority of MIBG scan for detection of primary tumor as well as bone metastases. However, MIBG is not always the most appropriate investigation, as shown by 11 observed pitfalls. Ten false negative cases have been observed and must be considered: in five out of 10 cases, bone scans performed with 99m Tc-HMDP made the diagnosis (3/7 cases of primary tumor and 2/3 cases of bone metastases). Moreover, one case was not usable due to a large digestive uptake. Our aim is to understand the reasons of the false negative by a meticulous analysis of every single case. The optimal procedure for neuroblastoma diagnosis, extent and follow up clearly seems to be the following strategy: MIBG scan must be firstly performed; in case of non-demonstrative scan the bone scan, which is complementary, will greatly contribute to the diagnosis.