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Endocrinological Oncology |
Department of Diabetes and Endocrine Services (J.R.B., A.D., T.M.G., L.H.) Royal Hobart Hospital, Department of Nuclear Medicine (R. W.), Royal Hobart Hospital; General Practitioner (J.P.); Department of Surgery (S.J.W.), University of Tasmania, Hobart, Tasmania
Address correspondence and requests for reprints to: L. Hoffman, M.D., F.R.A.C.P., Consultant Endocrinologist, Department of Diabetes and Endocrine Services, Royal Hobart Hospital, GPO Box 1061L, Tasmania, Australia 7001.
| Abstract |
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Aims: The objective of the present study was to examine an apparent heritable predisposition to PTC occurring in two Tasmanian families in which PTC occurs commonly.
Methods: Pedigree charts were constructed for both families and the medical records of the members reviewed.
Results: In Pedigree I, 7 of 25 members had PTC (6 of these had coexisting multinodular goiter (MNG), and 11 others had MNG. In Pedigree II, identical male twins and their daughters had PTC.
Conclusions: In both families there is evidence of autosomal dominant inheritance of PTC. The association of PTC with MNG suggests a possible role for MNG in tumor pathogenesis in hereditary PTC. The majority of the patients were diagnosed with PTC before commencement of prospective screening, indicating clinically relevant disease in the families described.
| Introduction |
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It is possible that environmental factors or random association may explain the occurrence of PTC in a proportion of these families. Some authors have postulated an autosomal dominant basis for familial PTC; however, the exact mode of inheritance remains obscure (4, 5, 9). Stoffer et al.(4) noted an increased occurrence of nonmalignant thyroid disease in some families with PTC, but the relationship between benign thyroid disease and the subsequent development of malignant papillary lesions was unclear.
We report two unrelated Tasmanian kindred in which PTC occurs commonly.
| Patients and Methods |
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| Results |
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A 62-yr-old female presented with a hoarse voice. A multinodular goiter (MNG) had been noted 2 yr previously. On examination, left vocal cord paralysis and a hard, left sided neck mass were detected. Neck exploration demonstrated locally invasive papillary carcinoma of the thyroid. The patient was treated with total thyroidectomy and 6000 MBq of radio iodine. No evidence of abnormal 131I uptake was noted on post-ablative whole body scans. Abnormal areas of thallium uptake in the neck and chest were noted, becoming less prominent on consecutive scans. She remains well.
Three of the patients six children presented with MNG in the ensuing
six months (Patients M, N, and P, Fig. 1
) and underwent
surgical resection. Surgical management was undertaken because of mild
compressive symptoms, a low thyrotropin level (indicating unsuitability
for thyroxine suppression), and patient anxiety. One patient had FNA of
the thyroid preoperatively that was nondiagnostic. PTC was detected
during pathological examination in all cases, one microscopic, one 10
mm in diameter, and the other multifocal PTC. On screening, one of the
patients six children (Patient O) had a solitary nodule confirmed as
PTC on excision. Screening other family members yielded two further
relatives with MNG who had multifocal PTC (Patients U and W). Patient U
had neoplasia suggested on preoperative FNA. Other relatives with
abnormal thyroid glands on screening are shown in Fig. 1
.
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There was no family history of colonic malignancy or intestinal polyposis and no history of radiation exposure.
Pedigree II
A 49-yr-old male presented with a 3-week history of left-sided
neck swelling. Examination revealed a 1.5 cm mass palpable in the left
lobe of the thyroid gland. The patients family history was
unremarkable for thyroid or bowel malignancy, and there was no history
of radiation exposure. Following ultrasound and isotope imaging (Fig. 1
), the patient underwent hemithyroidectomy, and histopathological
examination revealed papillary carcinoma. Total thyroidectomy was
subsequently performed, and the patient received a 6000 MBq dose of
radio iodine. Follow-up studies to 3 yr have not demonstrated disease
recurrence. One year subsequent to presentation of the index case, the
patients monozygotic twin brother presented with a neck mass,
assessment of which also revealed PTC, metastatic to a cervical lymph
node. In 1995, the 23-yr-old daughter (Patient K) of the index case
presented with a right sided thyroid mass, subsequently proven to be an
invasive 12 mm PTC. She was treated by total thyroidectomy, ablative
radio iodine, and thyroxine suppression. The 22-yr-old daughter of the
other twin (Patient L) had a MNG on screening, and a sclerosing
papillary microcarcinoma was found on resection. There has been no
evidence of recurrence in any of these family members. The family tree
for Pedigree II is also summarized in Fig. 1
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The characteristics of surgically treated thyroid disease from both
pedigrees are summarized in Table 1
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In this report we describe two kindred with a high prevalence of PTC. In both families, history and physical examination consistent with FAP or Cowdens syndrome was absent. In Pedigree I, 18 of 25 members had either PTC, multinodular goiter, or both. Although Pedigree II is less extensive, the development of PTC in monozygotic twins (within one year of each other) and in 2 of their offspring suggests an underlying genetic predisposition to thyroid neoplasia. The fact that both parents and a grandparent of the twins lived to an advanced age without evidence of thyroid cancer suggests the possibility of a de novo mutation occurring early in the twins embryogenesis.
Although a family history of thyroid cancer has been reported in up to 6.2% of patients presenting with PTC, the pedigrees in these reports are small, and a clear inheritance pattern is absent. Pedigree I represents one of the largest kindred with non-FAP familial PTC described thus far. The kindred exhibits an autosomal dominant pattern of PTC occurrence and a strong association with multinodular goiter. Historically, Tasmania is recognized as having a high prevalence of endemic goiter secondary to iodine deficiency (11). However, the prevalence of goiter in this population had fallen to less than 10% by 1975, following the introduction of public health measures that have rendered the community iodine replete (12). Thus, on the basis of this prevalence data the proportion of family members in Pedigree I with MNG is high.
An association may exist between iodine deficiency, multinodular goiter, and thyroid malignancy. However such an association is weak at best: a recent study detected PTC in only 2.2% of patients undergoing thyroidectomy for MNG (13). If a link between iodine deficiency and thyroid neoplasia does exist, it is unlikely to explain our observations, as the prevalence of follicular, rather than papillary, neoplasia is increased in this circumstance (3). It is possible that in this kindred MNG is a heritable condition, acting as a precursor to malignant disease. Existing evidence supports this contention, as thyroid malignancy is thought to be a multistep process. Furthermore, common genetic factors have been implicated in the pathogenesis of both MNG and PTC (9).
Among several possible oncogenes, the PTC/RET oncogene is a model a and putative candidate for the development of PTC in the families we describe (14, 15). Activating rearrangements of this oncogene have been identified in tissue from MNG and PTC, while they are typically absent in other neoplasms. Transgenic mice carrying the RET/PTC oncogene develop bilateral thyroid carcinoma with cellular features comparable to human PTC (15). Mutations of the RET proto-oncogene predispose to the development of multiple endocrine neoplasia type II and the associated medullary thyroid carcinoma (16).
Tissue samples from several patients will be analyzed for activating RET mutations. Incomplete penetrance of familial PTC may explain both the obligatory carrier status of patient C in Pedigree I and nonexpression of clinically overt thyroid disease. The influence of secondary modifying factors, such as gender, may explain this observation as in pedigree I, where six of seven patients with PTC are female. This observation is similar to that of Lote et al.(9), who described a female predilection for PTC in a Norwegian family.
Both families included individuals with multifocal PTC occurring at a young age, consistent with other reports of familial PTC (17). All patients to date appear to be cured, except for a small focus of thallium uptake in patient I(K), however the follow-up time is less than 4 yr.
The optimal strategy for investigation and management of kindred with PTC is unclear. Exclusion of occult FAP would seem prudent, however in the absence of a family history of bowel malignancy, or characteristic physical stigmata of Gardners syndrome, routine colonic assessment would seem unwarranted. The possible high risk of PTC developing in an underlying MNG, and the limited value of ultrasonography, isotope scanning, and FNA in excluding malignancy in this setting, argue strongly for thyroidectomy in family members of Pedigrees I and II who have evidence of MNG. The screening strategy recommended for these families is annual thyroid ultrasonography and neck palpation by an experienced examiner. Patients with evidence of goiter may then be counselled regarding the potential risk of malignancy and offered the option of early thyroidectomy.
| Conclusions |
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| Acknowledgments |
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Received August 12, 1996.
Revised November 12, 1996.
Accepted November 19, 1996.
| References |
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