Radiation-induced endocrine tumors

Can radiation induce pituitary tumors? Giant prolactinoma after radiation exposure

Radiation is a well-known etiology for many CNS tumors, including meningiomas, sarcomas and gliomas. However, occurrence of pituitary adenoma after radiation exposure is rare. We report a 21-year-old man with a pituitary adenoma, who was treated with post-operative radiotherapy for pontine glioma at 6 years of age. The role of radiation exposure in the etiology of pituitary adenoma is discussed, along with a literature review of radiation-induced tumors.

Cytohistologic correlation of thyroid nodules

BACKGROUND

Fine-needle aspiration (FNA) is widely used as a diagnostic tool to assess thyroid nodules. This study correlates FNA cytology results with surgical pathologic findings.

METHODS

All thyroidectomies performed between 1994 and 2004 were reviewed, identifying 242 patients. Data were obtained for FNA diagnosis, demographics, findings on ultrasound, and histologic findings.

RESULTS

Among 89 patients with a carcinoma on FNA, 89% of cases were verified on final histopathology. Of 78 patients with "follicular lesion" on FNA, only 36% of cases were verified to be malignant at surgery. Only 13% of the 75 cases diagnosed as benign, mostly colloid nodules, on FNA were found to have a carcinoma on histopathology.

CONCLUSION

A cytologic diagnosis of papillary carcinoma has a highly predictive of thyroid cancer. When dealing with follicular lesions the predictive value of FNA drops considerably. However, we found a 13% false positive result to occur in FNA declared benign lesions.

Absence of a specific radiation signature in post-Chernobyl thyroid cancers

Thyroid cancers have been the main medical consequence of the Chernobyl accident. On the basis of their pathological features and of the fact that a large proportion of them demonstrate RET-PTC translocations, these cancers are considered as similar to classical sporadic papillary carcinomas, although molecular alterations differ between both tumours. We analysed gene expression in post-Chernobyl cancers, sporadic papillary carcinomas and compared to autonomous adenomas used as controls. Unsupervised clustering of these data did not distinguish between the cancers, but separates both cancers from adenomas. No gene signature separating sporadic from post-Chernobyl PTC (chPTC) could be found using supervised and unsupervised classification methods although such a signature is demonstrated for cancers and adenomas. Furthermore, we demonstrate that pooled RNA from sporadic and chPTC are as strongly correlated as two independent sporadic PTC pools, one from Europe, one from the US involving patients not exposed to Chernobyl radiations. This result relies on cDNA and Affymetrix microarrays. Thus, platform-specific artifacts are controlled for. Our findings suggest the absence of a radiation fingerprint in the chPTC and support the concept that post-Chernobyl cancer data, for which the cancer-causing event and its date are known, are a unique source of information to study naturally occurring papillary carcinomas.

Follicular neoplasms of the thyroid: what to recommend

Follicular neoplasms of the thyroid are usually diagnosed following fine-needle aspiration (FNA) biopsy of a dominant thyroid nodule. An FNA diagnosis of a follicular neoplasm represents a heterogeneous group of lesions including benign follicular hyperplasia, follicular adenomas, follicular carcinomas, and the follicular variant of papillary carcinoma. Hürthle cell neoplasms are also often included in this group. Because the criteria for malignancy in both follicular and Hürthle cell neoplasms requires vascular or capsular invasion seen on permanent histology, the majority of these patients undergo surgical resection. Intraoperative frozen section analysis of follicular neoplasms rarely renders informative information. Approximately 20% of these lesions prove to be malignant and for lesions greater than 1.0 cm in size, the majority of surgeons and endocrinologists recommend a total thyroidectomy. Postoperative treatment generally includes therapeutic doses of 131I for follicular carcinomas.

Screening high-risk populations for thyroid cancer

BACKGROUND

Children treated with radiotherapy to the neck or exposed to environmental radiation are at risk for developing thyroid cancer later in life. The best method for screening these high-risk patients is unclear. We systematically reviewed evidence on the accuracy of ultrasound and palpation to detect thyroid nodules and of fine needle aspiration (FNA), a confirmatory test, to diagnose thyroid cancer.

PROCEDURE

We searched the MEDLINE database for papers published since 1966, using the MeSH term thyroid neoplasms and terms related to diagnostic test performance. To supplement our MEDLINE searches, we searched reference lists from recent reviews and articles recommended by thyroid cancer experts. We recorded the tests used, the gold standard determination of disease, the test performance results, and the presence of biases that could affect the reported results. We also abstracted the number of patients who underwent surgery and the final diagnoses. We created two decision models: one for screening 10,000 medically irradiated patients, and one for screening 10,000 environmentally irradiated patients.

RESULTS

Using ultrasound as the gold standard determination of the presence of a nodule, the sensitivity of palpation for all sized nodules was 10-41 percent, indicating that a high proportion of nodules detected by ultrasound are too small to be palpated. Sensitivity of palpation increased with nodule size. The specificity of palpation ranged from 95 to 100%. In studies from referral centers, the reported sensitivity and specificity of FNA were 71-95 and 52-99%, respectively. However, most authors excluded the proportion of patients (6-33%) who had inadequate or nondiagnostic FNA results when calculating sensitivity and specificity, even though 6-100% of these patients went on to have a diagnostic lobectomy. When each study was reanalyzed so that patients with nondiagnostic FNA results who went directly to surgery were reclassified as positive tests, sensitivity increased slightly, but specificity dropped by 4-20 percentage points per study. The decision model for screening 10,000 medically irradiated patients revealed that if ultrasound were used as an initial screen, 2,741 patients would have nodules at least 1 cm in size; assuming no patients with smaller nodules had surgery, 1,964 patients would have surgery; 275 patients would have a diagnosis of thyroid cancer. Screening with ultrasound as an initial test would detect an additional 150 cases of thyroid cancer compared to those screened with palpation. However, an additional 1,689 patients would have surgery for nonmalignant nodules (compared to 480 patients with nonmalignant nodules screened with palpation). The yield for screening 10,000 environmentally irradiated patients was several times smaller than for screening 10,000 medically irradiated patients. If 10,000 environmentally irradiated patients were screened initially with ultrasound, approximately 708 patients would have nodules at least 1 cm in size; 89 patients would have surgery; and 38 patients would be diagnosed with thyroid cancer.

CONCLUSIONS

Regardless of type of exposure, testing initially with ultrasound detects several times more cases of thyroid cancer than palpation. However, when ultrasound is the initial test, many more patients also have surgery for nonmalignant nodules. Screening with palpation is not very reassuring, particularly to medically irradiated patients with negative tests, since almost half (46%) of these patients may have undetected nodules.

Radioiodine-induced thyroid cancer: Studies in the aftermath of the accident at Chernobyl

While a great deal is known about the relationship between external radiation exposure and thyroid cancer, much less is known about the oncogenic effects of internal radiation exposure from isotopes of iodine. The accident at the Chernobyl nuclear power plant released massive quantities of radioiodine isotopes into the atmosphere. The large number of ensuing thyroid cancers in exposed children leaves little doubt that these malignancies have occurred as a result of the accident. However, carefully planned epidemiological studies are needed to confirm that these are due predominantly to I-131 exposure, to determine the dose-response relationship, to monitor for continuing effects and to evaluate other contributing factors. Preliminary evidence indicates that there is a distinct pattern of somatic genetic changes in the thyroid cancers from the Chernobyl area.