Functioning Insulinoma—Incidence, Recurrence, and Long-Term Survival of Patients: A 60-Year Study

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For the 60-year period from 1927 through 1986, we assessed the incidence, recurrence, and long-term survival among all Mayo Clinic patients with histologically confirmed functioning insulinoma. With use of the complete medical record system at Mayo and the comprehensive epidemiologic data base of residents of Olmsted County, Minnesota, we found 224 patients in whom an initial pancreatic exploration at Mayo had confirmed the presence of insulinoma. The median age (and range) of these patients at surgical diagnosis was 47 (8 to 82) years, and 59% were female patients. During the study period, eight cases of insulinoma occurred among residents of Olmsted County; their age and gender distributions were similar to those of the total cohort. The incidence of insulinoma among residents of Olmsted County increased during the study period to a stable level during the last 2 decades of 4 cases per 1 million person-years. For the total cohort, 7.6% had multiple endocrine neoplasia type I (MEN I), and 5.8% had malignant insulinoma. The risk of recurrence was greater among patients with MEN I (21% at 10 and 20 years) than in those without MEN I (5% at 10 years and 7% at 20 years). Although survival of the total cohort was not significantly impaired, it was significantly worse than expected for patients with malignant insulinoma (29% versus 88% expected at 10 years postoperatively). We conclude that insulinoma is less rare than previously suspected. After successful surgical removal, the long-term risk of recurrent insulinoma is relatively high in patients with MEN I; for patients with benign disease, the long-term survival is normal.

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Study Population.

To identify the study cohort, we reviewed the entire medical records of all patients with histologically confirmed insulinoma for the period from the first identified case in 1927 through 1986. Although some of these records had been reviewed previously for other purposes,2, 15, 16, 17, 18, 19 this report represents the only comprehensive assessment of all patients with insulinoma at the Mayo Clinic during 6 decades for the purpose of determining the epidemiologic features of this disorder.

Distribution of Cases by Age, Gender, and Period of Study.

For the total cohort of patients (N = 224), the median age (and range) at the time of surgical diagnosis was 47 (8 to 82) years, and 59% were female patients (Table 1). We found no evidence that age or gender distribution among Mayo Clinic patients with insulinoma varied during the study period (1927 through 1986). In addition, no difference was noted between male and female patients with respect to age or year of histologic diagnosis.

Incidence of Insulinoma in Olmsted County.

During the 6-decade period of observation, eight cases of

DISCUSSION

Before this study, data about the incidence of insulinoma in a geographically defined population, the risk of recurrence of insulinoma, and the long-term survivorship of patients with insulinoma were not available. With such knowledge, primary-care physicians, internists, endocrinologists, neurologists, and psychiatrists who must recognize the disorder, radiologists who attempt to localize the lesions, surgeons who remove them, and oncologists who treat malignant insulinomas would be better

CONCLUSION

Insulinoma is a rare disorder with an estimated incidence of 4 cases per 1 million person-years; however, it is less rare than previously suspected. The risk of recurrence of this disorder spans 2 decades and is high among patients with MEN I. After successful removal of the insulinoma, cure can be anticipated in most patients. For those with benign insulinoma, a normal life span can be expected after successful surgical resection.

ACKNOWLEDGMENT

We thank Margaret Telander for collection of the study data, C. Mary Beard for supervision of data collection and follow-up, Chu-Pin Chu for assistance in data analysis, and Sondra L. Buehler for assistance in the preparation of the submitted manuscript.

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    This study was supported in part by Research Grant AR 30582 from the National Institutes of Health, Public Health Service. Dr. Ballard is supported in part by a Career Development Award from the Merck, Sharp & Dohme/Society for Epidemiologic Research Clinical Epidemiology Fellowship Program.

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