Papillary thyroid carcinoma in a boy with familial tuberous sclerosis complex attributable to a TSC2 deletion-a case report

Chromophobe renal cell carcinoma-like thyroid carcinoma: possible misdiagnosis as metastatic renal cell carcinoma

To date, multiple thyroid cancer variants have been reported. Herein, we report a rare case of chromophobe renal cell carcinoma-like thyroid carcinoma (CRETHCA) in a 60-year-old woman, for which the morphologic findings resembled those of chromophobe renal cell carcinoma (ChRCC). ChRCC of the kidney is characterized by large polygonal tumor cells with distinct cell borders, perinuclear clearing, multiple binucleate cells, and strongly positive immunostaining for paired box gene 8 (PAX8) and carbonic anhydrase IX (CA IX). In our case, the thyroid gland tumor was incidentally detected by routine medical screening without sufficient medical information; it showed similar histology and immunohistochemical features to ChRCC and was initially misdiagnosed as metastatic ChRCC. Additional tests, including kidney computed tomography and positron emission tomography, revealed no abnormalities in the patient's kidney; therefore, we diagnosed the tumor as CRETHCA. Focal weak staining for thyroid transcription factor 1 (TTF-1) was the only supporting evidence that it was a primary thyroid neoplasm. To the best of our knowledge, this is the second report of CRETHCA in literature. This novel variant is very difficult to distinguish from metastatic ChRCC and can be a diagnostic challenge for pathologists. Further studies of similar cases should be done to define this new entity.

Eosinophilic Solid and Cystic (ESC) Renal Cell Carcinomas Harbor TSC Mutations: Molecular Analysis Supports an Expanding Clinicopathologic Spectrum

Eosinophilic solid and cystic (ESC) renal cell carcinoma (RCC) has recently been described as a potentially new subtype of RCC based upon morphologic and immunohistochemical features. These neoplasms typically demonstrate solid and cystic architecture, and the neoplastic cells contain voluminous eosinophilic cytoplasm with granular cytoplasmic stippling. There is frequently focal immunoreactivity for cytokeratin 20. Although the initial cases all occurred in adult females and had benign outcome, we recently expanded the proposed spectrum of this neoplasm to include pediatric cases, multifocal neoplasms, and a case with hematogenous metastasis. ESC has been postulated to be analogous to a subtype of RCC consistently identified in tuberous sclerosis complex patients, and while previous work has demonstrated loss of heterozygosity at the TSC1 locus and copy number gains at TSC2 in ESC RCC, these genes have not been sequenced in ESC RCC. Using capture-based and amplicon-based next-generation sequencing, we now demonstrate the consistent presence of either TSC1 or TSC2 gene mutations in pediatric ESC RCC (8/9 cases) and adult ESC RCC (6/6 cases). These included a metastatic ESC RCC which had a complete response to mTOR targeted therapy. We also found these mutations in some neoplasms with variant morphology and thus potentially expand the spectrum of ESC RCC. These include one of our adult cases which demonstrated dominant "type 2" papillary RCC morphology and 2 of 3 previously unclassified pediatric RCC with features of ESC RCC minus granular cytoplasmic stippling. We also demonstrate TSC mutations in a case of so-called "oncocytoid RCC after neuroblastoma" with identical morphology and immunoprofile, providing a molecular link between the latter and ESC RCC. In summary, ESC RCC consistently harbors actionable TSC1 or TSC2 mutations, which are infrequently seen in established subtypes of RCC. These findings support TSC1/2 mutation as a molecular marker of ESC RCC, and suggest expansion of the clinicopathologic spectrum to include neoplasms with papillary architecture, occasional cases lacking well-developed granular cytoplasmic stippling, and a subset of RCC with oncocytic features in patients who have survived neuroblastoma.

Less common manifestations in TSC

Tuberous sclerosis complex (TSC) is due to pathogenic variants in TSC1 or TSC2 genes resulting in hyperactivation of the mTOR pathway. Many organ systems can be affected, such as brain, skin, eye, heart, bone, kidney, or lung. Typical lesions of TSC usually are those included as major criteria, including angiofibromas, hypomelanotic macules, tubers, subependymal nodules, angiomyolipomas, cardiac rhabdomyomas, and lymphangioleiomyomatosis. However, there are many other manifestations less frequent and/or less well known, many of them not included as clinical diagnostic criteria that are part of the clinical spectrum of TSC. The focus of this review will be on these less common and less well-known manifestations of TSC. Among the rare manifestations, we will discuss some clinical findings including arteriopathy, arachnoid cysts, lymphatic involvement, chordomas, gynecological, endocrine, and gastrointestinal findings. Among the manifestations that are very frequent but much less well known, we find the sclerotic bone lesions. Although they are very frequent in TSC they have been largely overlooked and not considered diagnostic criteria, mainly because they are asymptomatic. However, it is important to know their typical characteristics to avoid misdiagnosing them as metastasis.