Syndrome de Birt-Hogg-Dubé et tumeurs multiples récidivantes

FLCN Variants in Parathyroid Carcinoma and Atypical Parathyroid Tumors

Parathyroid carcinoma (PC) and atypical parathyroid tumors (APT) are incompletely understood and pose challenges in definitive diagnosis. FLCN sequence variants have recently been linked to PC and APT. Inactivating mutations in the ubiquitously expressed FLCN tumor suppressor gene, encoding folliculin, cause Birt-Hogg-Dubé syndrome (BHD), a rare tumor predisposition syndrome. Germline inactivating FLCN variants, accompanied by somatic allelic loss, were reported in 2 unrelated patents with PC, both with clinical features, but no diagnosis, of BHD. Somatic frameshift variants of likely pathogenicity were reported in 1 patient with PC and 1 with APT. On the other hand, neither PC nor APT has been reported in sizeable BHD series. To better understand the frequency of FLCN variants in PC and APT, we analyzed a series of 10 patients with sporadic PC and 14 with APT by direct Sanger DNA sequencing. We identified no inactivating FLCN mutations in any of the PC or APT samples examined. A germline missense variant (p.Gly325Val), predicted as benign/tolerated, was seen in 1 PC and a synonymous variant in 1 APT. The absence of pathogenic mutations detected in our series of PC and APT further suggests that FLCN variants are rare in these tumors. Nevertheless, the potential roles of FLCN in the pathogenesis of PC and APT merits further consideration and study.

Germline- and Somatic-Inactivating FLCN Variants in Parathyroid Cancer and Atypical Parathyroid Tumors

CONTEXT

Parathyroid cancer (PC) is a rare endocrine neoplasm with high mortality. While surgery is the treatment for patients with the disease, recurrence rates are high, and patients usually succumb to severe hypercalcemia. There is no effective systemic therapy for the disease.

OBJECTIVE

To investigate for novel genes causing parathyroid cancer.

METHODS

We analyzed the germline DNA of 17 patients with "sporadic" PC and 3 with atypical parathyroid tumors (APTs) who did not have germline CDC73 or MEN1 pathogenic variants. Sequencing of available tumor tissue from 14 patients with PC and 2 with APT was also performed (including 2 patients with no available germline DNA). In addition, sporadic parathyroid adenomas from 74 patients were analyzed for FLCN variants.

RESULTS

We identified germline FLCN variants in 3 unrelated patients with PC. The 2 frameshift variants have been described in patients with Birt-Hogg-Dubé (BHD) syndrome, while the pathogenicity of the missense variant c.124G > C (p.G42R) has not been definitively established. Functional analysis of the missense variant showed a potential effect on posttranslational modification. All 3 patients with germline FLCN variants were noted to have renal cysts and 2 had lung cysts, features associated with BHD syndrome. Somatic FLCN variants were identified in tumors from 2 (1 APT) of 16 patients with PC/APT and in none of the 74 sporadic parathyroid adenomas. No second hits in FLCN were noted on sequencing; however, loss of heterozygosity at the locus was demonstrated in 2 of 3 patients with the identified germline FLCN variant.

CONCLUSION

The finding of FLCN variants associated with PC may provide the foundation for the development of therapy for this malignancy.

Oncocytic carcinoma of the parotid gland as a manifestation of Birt-Hogg-Dube syndrome

Renal oncocytomas are commonly reported in association with Birt-Hogg-Dube (BHS) syndrome, while BHD-associated oncocytomas of the parotid gland are rare. To date, there have been only 11 cases of BHD-associated parotid gland oncocytoma, without a reported case of malignant transformation. We present the first reported case of oncocytic carcinoma of the parotid gland associated with BHD, with radiologic and histologic correlation. This case establishes that BHD-associated parotid oncocytic lesions, previously identified only as benign oncocytomas in the literature to date, can undergo malignant transformation, and should potentially be regarded with a higher index of suspicion and lower threshold for aggressive management.

Colorectal cancer risk in families with Birt-Hogg-Dubé syndrome increased

OBJECTIVE

Birt-Hogg-Dubé syndrome (BHDS) is an inherited tumour syndrome characterised by three major symptoms: lung cysts with spontaneous pneumothorax, fibrofolliculoma and renal cell cancer. The first family with this syndrome was described in 1975 and one of its members presented with adenomatous colon polyps and colorectal cancer. Since then, it has been a matter of debate whether colorectal cancer is indeed part of the BHDS spectrum and if regular screening should be recommended.

DESIGN

We analysed the frequency of colorectal cancer in a large sample of BHDS families. Clinical data were available from 256 BHDS patients (male 130, female 126) belonging to 83 unrelated families. For controls, 83 index patients who attended our outpatient clinic for non-malignancy-related genetic counselling and their family members (total of 519 controls) were used.

RESULTS

The patients with BHDS showed a moderately but significantly increased rate of colorectal cancer (5.1% versus 1.5%, p-value .0068). Unexpectedly, 35% of patients with colorectal cancer corresponding to eight of 82 BHDS families fulfilled the revised Bethesda criteria for HNPCC, either because colorectal cancer occurred before age 50 years or because three family members were affected by colorectal cancer. Apart from colorectal cancer, no other HNPCC-associated tumours occurred within the Bethesda criteria-positive families, an observation that argues against a concurrence of BHDS and HNPCC in these families.

CONCLUSION

The results suggest that BHDS is associated with early-onset colorectal cancer, a hypothesis that might have a marked impact on preventive screening recommendations.