AN EVALUATION OF COMPOSITE PATTERNS OBSERVED IN 2 GASTRIC CARCINOIDS

Background. Varying composite patterns found in gut-endocrinomas (carc inoids) were investigated for their possibility of clarifying the mech anism of the histogenesis of such tumors in relation to ordinary carci nomas, Methods. Multiple serial sections of two composite lesions in t he stomach were scrutinized by histology, silver impregnations, immuno histochemistry and electron microscopy, and each section of the lesion s was carefully reconstructed in three-dimensional aspect to clarify t he precise composite structures. Results. The two composite lesions we re composed of an admixture of 1) a carcinoidal portion with varying G rimelius-positivity (strongly positive to genative) and with several g rowth patterns (Types A, B and D); and 2) practically Grimelius-negati ve adenocarcinomatous portions of a papillotubular structure (Case 1) or of glandular/pseudoglandular architecture (Case 2), These two porti ons exhibited at low magnification clear-cut boundaries in most areas, but at high magnification displayed occasional transitional changes ( composite A pattern) and mixed structures, Transitional zones with suc h changes as well as the carcinomatous portions contained occasional g landular structures composed of Grimelius-positive cells (composite B pattern). Immunohistochemistry revealed a distribution of chromogranin -positive cells in accordance with Grimelius-positive cells in both ca rcinoidal and carcinomatous portions. Electron microscopic features of these two portions as compared with light microscopic findings indica ted that Grimelius-negative portions of the lesions as well as solid o r undifferentiated areas with only a few scattered Grimelius-positive cells (composite C pattern) contained a significantly greater number o f neoplastic cells with endocrine type granules. Conclusions. A wide s pectrum of various composite patterns found in the transitional zones between typical carcinoid and adenocarcinoma structures led us to cate gorize the composite patterns and postulate the histogenesis of the ca rcinoids as gut-endocrinomas and ordinary carcinomas, both originating from a primordial phase of carcinogenesis. It was then speculated tha t certain stimuli to neoplastic formation during the multidirectional phase (M-phase) prior to the unidirectional phase (U-phase) in stages of carcinogenesis could have resulted in various composite patterns, n ot only in a complex admixture of carcinoid-cardinoma structures but e ven in carcinoid structures with mixed patterns. It was pointed out th at, on the basis of a discrepancy between light microscopic and electi on microscopic findings, the concept of composite carcinoids might be modified or even revised in accordance with the latter findings, and t hat neoplasms with such structures might be more adequately called com posite gut-endocrinomas rather than carcinoids.