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Primary Localization of an Ectopic ACTH-Producing Bronchial Carcinoid Tumor by Indium ¹¹¹Pentetreotide Scintigraphy—Authors’ Response

National Institutes of Health Bethesda, Maryland 20892-1832

Dr. M. Reincke’s letter (above) illustrates an important principle in the development of diagnostic tests—results from additional patients should be reported to evaluate the validity of the conclusions from earlier studies. In the case (1) and Dr. Tabarin’s group (2), reported on 30 patients undergoing ¹¹¹Indium pentetreotide scintigraphy as well as conventional computed tomography (CT) and magnetic resonance (MR) examination to localize an ectopic ACTH-producing tumor. Both studies demonstrated that conventional imaging had superior sensitivity and fewer false positive results compared to scintigraphy. Furthermore, only one patient’s tumor was detected by scintigraphy alone (although subsequent CT confirmed the mass). In our study 7 of 17 positive scintigrams were falsely positive; of these, 4 were associated with nonendocrine lesions, such as fibrosis, on MR or CT scans. However, 3 required additional diagnostic tests and included a lesion that was not present on subsequent scintigraphy. Scintigraphy was the first correct indication of a tumor in 1 patient in Dr. Tabarin’s study and was falsely positive in 1 patient. Both articles concluded that conventional imaging should be the first line approach to detection of these tumors and that scintigraphy is an adjunctive modality.

Dr. Reincke’s patient illustrates that scintigraphy may detect a tumor that is not seen by conventional studies and that surgical exploration based on scintigraphy results can be successful. If we integrate this new information with the earlier results, positive octreotide scintigraphy correctly identified a tumor in only 2 of 10 patients when conventional imaging was negative. Given the difficulty in finding these ectopic ACTH-secreting tumors, octreotide scintigraphy may help find the needle in the haystack, as Drs. de Herder and Lamberts suggest (3). However, it may also lead to inappropriate surgery if a falsely positive scan is taken to represent tumor. Thus, we would sound a note of caution. When ¹¹¹Indium pentetreotide scintigraphy is the only positive imaging study, the risks of unsuccessful surgery should be weighed against the risk of alternative therapeutic approaches. Serious consideration should be given to medical management of hypercortisolism with subsequent conventional imaging to confirm the tumor.

Footnotes

Address correspondence to: David J. Torpy, M.D., Developmental Endocrinology Branch, NICH/HD, Building 10, Room 10N262, 10 Center Drive, Bethesda, Maryland 20892-1832.

Received June 17, 1999.

References

1. Torpy DJ, Chen CC, Mullen N, et al. 1999 Lack of utility of ¹¹¹ In-pentetreotide scintigraphy in localizing ectopic ACTH-producing tumors: Follow-Up of 18 Patients. J Clin Endocrinol Metab. 84:1186–1192.[Abstract/Free Full Text]
2. Tabarin A, Valli N, Chanson P, et al. 1999 Usefulness of somatostatin receptor scintigraphy in patients with occult ectopic adrenocorticotropin syndrome. J Clin Endocrinol Metab. 84:1193–1202.[Abstract/Free Full Text]
3. de Herder WW, Lamberts SWJ. 1999 Editorial: Tumor localization—The ectopic ACTH syndrome. J Clin Endocrinol Metab. 84:184–185.[Abstract/Free Full Text]

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