Kidney cancer. Principles and practice. Second edition. Primo N. Lara, Jr. Eric Jonasch (Editors). Springer International Publishing (2015)

BHD was discovered by a group of Canadian dermatologists in 1977. Their study of an extended family revealed 15 out of 37 members after the age of 25 developing fibrofolliculomas and associated trichodiscomas or acrochordon (Fig. 8.4) [38]. The fibrofolliculomas were extension of epithelial strands beyond the infundibulum of the hair follicles. The incidence of BHD was noted to be 1 in 200,000 and transmitted in an autosomal dominant fashion. Further linkage analysis confirmed the gene location to 17p11.2 [39], which encodes for folliculin (FLCN). The gene in question behaves like a classic tumor suppressor and was found to participate in a complex that regulates downstream functions of AMPK and mTOR [40, 41]. Hasumi and colleagues determined loss of FLCN-upregulated activities of mTORC1 and mTORC2 [42].

__Kidney Cancer_ Principles and Practice-Springer International Publishing (2015) 8.4

Fig. 8.4. Image of left neck of an individual with BHD demonstrating multiple small fibrofolliculomas

__Kidney Cancer_ Principles and Practice-Springer International Publishing (2015) 8.5

Fig. 8.5. A PET/CT imaging from a 9 cm left paraganglioma above the kidney and adjacent to the superior mesenteric artery. The patient had anxiety and intermittent mood swings due to massively elevated catecholamines. The family history was significant for a GI stromal tumor, and he was found with an SDHB alteration

In addition to the skin manifestations that are pathognomonic to BHD, the affected individuals also have a greater than 50-fold increase risk in lifetime pneumothoraces, a likely sequela of their propensity in developing lung cysts [43]. After adjusting for age, those with BHD were about seven times more likely to develop renal tumors [43]. With an average onset of age 50, renal lesions in the setting of BHD tend to be bilateral and multifocal in their occurrence [44–46]. The most common tumor in BHD is a hybrid oncocytic neoplasm, which contains both chromophobes with oncocytic features [47]. These tumors tend to have better prognosis due to their relatively indolent progression: less than 5% of affected individuals go on to develop metastatic disease [48]. Clear cell and papillary histologic subtypes are found in less than 10% of tumors, but when present, they portend a significantly worse prognosis.

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