Population-based study of familial medullary thyroid cancer

Inherited variants in genes somatically mutated in thyroid cancer

Background

Tumour suppressor genes when mutated in the germline cause various cancers, but they can also be somatically mutated in sporadic tumours. We hypothesized that there may also be cancer-related germline variants in the genes commonly mutated in sporadic well-differentiated thyroid cancer (WDTC).

Methods

We performed a two-stage case-control association study with a total of 2214 cases and 2108 healthy controls from an Italian population. By genotyping 34 single nucleotide polymorphisms (SNPs), we covered a total of 59 missense SNPs and SNPs located in the 5' and 3' untranslated regions (UTRs) of 10 different genes.

Results

The Italian1 series showed a suggestive association for 8 SNPs, from which three were replicated in the Italian2 series. The meta-analysis revealed a study-wide significant association for rs459552 (OR: 0.84, 95%CI: 0.75–0.94) and rs1800900 (OR: 1.15, 95%CI: 1.05–1.27), located in the APC and GNAS genes, respectively. The APC rs459552 is a missense SNP, located in a conserved amino acid position, but without any functional consequences. The GNAS rs1800900 is located at a conserved 5'UTR and according to the experimental ENCODE data it may affect promoter and histone marks in different cell types.

Conclusions

The results of this study yield new insights on WDTC, showing that inherited variants in the APC and GNAS genes can play a role in the etiology of thyroid cancer. Further studies are necessary to better understand the role of the identified SNPs in the development of WDTC and to functionally validate our in silico predictions.

Surgery for thyroid cancer

The incidence of thyroid cancer, particularly papillary thyroid cancer, is rising at an epidemic rate. The mainstay of treatment of most patients with thyroid cancer is surgery. Considerable controversy exists about the extent of thyroid surgery and lymph node resection in patients with thyroid cancer. Surgical experience in judgment and technique is required to achieve optimal patient outcomes.

Risk of thyroid cancer in relatives of patients with medullary thyroid carcinoma by age at diagnosis

The familial risk of medullary thyroid carcinoma (MTC alone or as part of multiple endocrine neoplasms, MEN2A/MEN2B) is high, so we aimed to answer open questions about the lifetime cumulative risk of thyroid cancer (LCRTC at 0-79 years) among relatives of MTC patients by age and sex. For this nationwide study, a cohort of 3217 first-/second-degree relatives (FDRs/SDRs) of 389 MTC patients diagnosed in 1958-2010 in the Swedish Family-Cancer Database was followed for the incidence of thyroid cancer. The LCRTC in female relatives of patients with early-onset MEN2B (diagnosis age <25 years) was 44-57%, representing 140-520 times increase over the risk in their peers without a family history of endocrine tumors (men: LCRTC=22-52%, 320-750 times) depending on the number of affected FDRs/SDRs. The LCRTC in female relatives of patients with late-onset MEN2B (diagnosis age ≥25 years) was about 15-43% (men=24%). The LCRTC among relatives of early-onset MTC-alone patients was 3-20%. The LCRTC among relatives of late-onset MTC-alone patients was 5-26%. The LCRTC in female relatives of MEN2A patients was 16-63% (men=52%). The relatives of patients with early-onset MTC exhibited a high tendency to develop early-onset thyroid cancer. Simply available data on the number of FDRs and even SDRs affected with MTC and their age at diagnosis were quite informative for the estimation of the risk of thyroid cancer in probands. In settings where genetic testing is not available or affordable for all, evidence-based cumulative risks reported in this nationwide study may help physicians to identify very high-risk individuals.

MicroRNAs in thyroid cancer

CONTEXT

Traditionally, factors predisposing to diseases are either genetic ("nature") or environmental, also known as lifestyle-related ("nurture"). Papillary thyroid cancer is an example of a disease where the respective roles of these factors are surprisingly unclear.

EVIDENCE ACQUISITION

Original articles and reviews summarizing our current understanding of the role of microRNA in thyroid tumorigenesis are reviewed and evaluated.

CONCLUSION

The genetic predisposition to papillary thyroid cancer appears to consist of a variety of gene mutations that are mostly either of low penetrance and common or of high penetrance but rare. Moreover, they likely interact with each other and with environmental factors. The culpable genes may not be of the traditional, protein-coding type. A limited number of noncoding candidate genes have indeed been described, and we propose here that the failure to find mutations in traditional protein-coding genes is not coincidental. Instead, a more likely hypothesis is that changes in the expression of multiple regulatory RNA genes, e.g. microRNAs, may be a major mechanism. Our review of the literature strongly supports this notion in that a polymorphism in one microRNAs (miR-146a) predisposes to thyroid carcinoma, whereas numerous other microRNAs are involved in signaling (mainly PTEN/PI3K/AKT and T3/THRB) that is central to thyroid carcinogenesis.

A Korean family of familial medullary thyroid cancer with Cys618Ser RET germline mutation

Familial medullary thyroid carcinoma (FMTC) is caused by autosomal dominant gain-of-function mutations in the RET proto-oncogene. An identifiable RET mutation can be detected in about 85% of FMTC families. The majority of germline mutations in FMTC have been found in exons 10 and 11 of the RET proto-oncogene, specifically within the cysteine codons 609, 611, 618, 620, and 634. We screened members of a large Korean family that had a history of FMTC by genetic analyses, and propose a therapeutic approach for managing the disorder. We report a RET mutation in exon10, codon 618 that causes substitution of a cysteine by a serine in the cysteine-rich domain of the RET receptor in a three-generation FMTC family composed of 30 members with 11 carriers. Nine of the gene carriers were clinically affected. The FMTC with cysteine RET mutations found in the Korean population is consistent with the clinical pattern reported worldwide; to date there have been no ethnic differences identified for FMTC. Our results suggest that this genetic profile might be associated with usually aggressive clinical course with regional lymph node metastasis but late onset of MTC.

Medullary Thyroid Cancer

The goal in managing patients who have MTC is to detect and surgically remove disease at an early stage. Tumor marker-based biochemical screening and DNA-based genetic screening have created the opportunity for effective prophylactic surgery in patients at risk for hereditary MTC. Complete surgical resection is critical for cure because cervical reoperation for persistent or recurrent disease benefits only select patients. With the advent of therapies that target the RET-activated pathways, new hope may be emerging for patients who have locally advanced or metastatic disease.

Familial risks for nonmedullary thyroid cancer

CONTEXT

Reliable data on familial risks are important for clinical counseling and cancer genetics.

OBJECTIVE

We wanted to define familial risks for histopathology-specific nonmedullary thyroid cancers through parental and sibling probands.

SETTING

The study examines the nationwide Swedish Family-Cancer Database on 10.5 million individuals, containing families with parents and offspring.

PATIENTS

Cancer data were retrieved from the Swedish Cancer Registry from years 1958 to 2002, including 3292 patients with thyroid adenocarcinoma. The Systematized Nomenclature of Medicine histology was available from 1993 onward, with 1449 papillary, 288 follicular, 148 anaplastic, and 68 Hurthle cell tumors.

MAIN OUTCOME MEASURES

Familial risk for offspring was defined through standardized incidence ratio, adjusted for many variables.

RESULTS

The familial risk for papillary carcinoma was 3.21 and 6.24 when a parent and a sibling, respectively, were diagnosed with thyroid cancers. There was an apparent gender preference, particularly among sisters, whose risk was 11.19. The risks were highest for early onset cancers. Thyroid adenocarcinoma was shown to be associated with melanoma and connective tissue tumors, and probably also with neurinomas (schwannomas). Associations found in single comparisons with papillary thyroid cancer and other sites included right-sided colon, breast, ovarian, and kidney cancers. Hurthle cell tumors were associated with Hodgkin's and non-Hodgkin's lymphoma, but the numbers of cases were small.

CONCLUSIONS

The present findings were based on a limited number of cases, but they display a complex and heterogeneous pattern of familial nonmedullary thyroid cancer. The high risk for papillary carcinoma among women requires clinical attention, although the absolute risks for this rare cancer are still low.

Familial risk of cancer by site and histopathology

Familial risks for histopathology-specific cancers have not been determined. We used the nationwide Swedish Family-Cancer Database on 10.2 million individuals and 1 million tumors to calculate standardized incidence ratios (SIRs) for familial cancers of specific histology and morphology among 0- to 66-year-old offspring. We used histology codes for both offspring and parents, but because of the limited number of cases, the morphology-specific classification could be used only for offspring by all site-specific cancers in parents, resulting in inflated risk estimates. A number of novel findings emerged in the histopathology-specific analysis of familial risks, in addition to some known associations. Overall, specific histology showed an SIR of 2.07 for all cancers compared to an SIR of 2.00 for any histology. However, the small effect was due to breast and prostate cancers, which showed a negligible effect of specific histology. Familial risks of over 4.0 were found for serous papillary cystadenocarcinoma of the ovary, papillary thyroid cancer and low-grade astrocytoma. Familial risks of over 3.0 were found for signet-ring gastric cancer, various forms of ovarian cancer and squamous cell skin cancer. Also noteworthy were familial risks of hepatocellular carcinoma (2.48), pancreatic adenocarcinoma (1.92), large cell carcinoma and adenocarcinoma of the lung (2.29 and 2.18, respectively) and clear cell carcinoma of the kidney (2.73). Many of the findings were novel and could be revealed only by applying codes for specific histopathology. These data call for a closer description of familial aggregations and probing for the underlying genetic mechanisms.

Gender effects in familial cancer

Very limited data are available on sex ratios in familial cancer. Such data would be valuable in the assessment of sex chromosome effects and of interactions between background and familial rates. We used the nationwide Swedish Family-Cancer Database on 10.2 million individuals and over 1 million neoplasms to analyze familial risks for male and female offspring by paternal and maternal concordant cancer. Sex ratios for familial cancer were derived for cancer at 15 sites shared by men and women. At 14 sites the sex ratio (male/female) for familial relative risk ranged between 0.78 and 1.41, with no evidence of sex preference, suggesting that sex chromosomes do not contribute to a noticeable extent to familial risks. Furthermore, in cancers where the background incidence varied extensively by sex, such as bladder cancer (sex ratio 2.82) and nonthyroid endocrine tumors (0.65), the familial effect was proportionate to the background incidence and the familial sex ratio was close to unity. In thyroid cancer, the familial sex ratio was 2.48 (1.54-3.98) and the background incidence ratio was 0.31. This was the first evidence of an inverse sex ratio in primary cancer, i.e., higher familial risk in the gender of low background risk. The high familial ratio, 2.85 (95% CI: 1.35-6.03), was due to thyroid adenocarcinoma, encompassing both papillary and follicular types.