Both carboxy and amino terminal fragments of mesothelin have been reported to be released from cells and are detectable in supernatants and sera of tumor bearing mice or humans [21–23, 25], it seems likely that the 49 kDa form represents the carboxy terminal fragment and the 34 kDa fragment is the amino terminal portion of the mesothelin, however it is possible that the 34 kDa form is a degradation product missing the amino acid sequence used to elicit the antisera (Fig. 1). This evidence concerns the gene MSLN and neoplasm.