Neuroendocrine tumors and their association with rare tumors: observation of 4 cases.

PURPOSE Neuroendocrine tumors are rare neoplasms, with an incidence of about 1/100,000/year. The association between digestive neuroendocrine tumors and epithelial tumors is known, accounting for about 10% of cases, whilst in a very small number of other cases an association with other low incidence tumors has been observed. METHODS During the past 19 years the Rare Hormonal Tumors Group of the Istituti Ospitalieri in Cremona, Italy has observed 300 patients affected by neuroendocrine tumors. We report here on four cases in which there was an unusual association with other rare neoplasms. RESULTS Overall, four of the 300 observed cases (1.3%) showed an unusual association with rare nonepithelial neoplasms: (1) gastric carcinoid and glioblastoma multiforme; (2) Merkel cell tumor and squamous cell carcinoma of the skin; (3) medullary thyroid carcinoma, yolk sac tumor of the testis and gastrointestinal stromal tumor (GIST); (4) gastric carcinoid and gastrointestinal stromal tumor (GIST). DISCUSSION There cases are of interest not only from an epidemiological point of view, but also offer insight into possible geno-phenotypical implications. The c-kit expression, typical of GISTs but observed also in other epithelial and neuroendocrine tumors, not only broadens the possibility to gain insight into the carcinogenesis of these neoplasms, but also opens the field to possible new therapeutic opportunities using multitargeted molecules. The contemporaneous presence of other lesions, such as the Merkel cell tumor and the squamous cell carcinoma of the skin can be interpreted as an answer by the cell to the same mutagenic stimulus. In other cases, where a possible link is not yet found which could explain the synchronism or metachronism of low incidence neoplasms, it remains possible that the associations are entirely coincidental. We await for new instruments which could help us demonstrate the possible relationships between low incidence neoplasms.