Thyroid follicular carcinoma-like renal tumor: a case report with morphologic, immunophenotypic, cytogenetic, and scintigraphic studies

A rare case of thyroid-like follicular carcinoma of the kidney in a 75-year-old male: Case report and review of the literature

INTRODUCTION AND SIGNIFICANCE

The presence of thyroid-like follicular carcinoma in the kidney is very rare, There have been few documented cases of this tumor's formation, and there are no specific signs for this tumor's presence and it is often discovered incidentally by chance, and the diagnosis depends mainly on histological examination and the negative results of thyroid marker tests.

CASE PRESENTATION

We describe the case of an adult male who had prostate adenocarcinoma and later suffered from pain in the flank, so radiographic examination showed a mass in the right kidney, which was removed, and the result of histopathologic examination was thyroid-like follicular carcinoma of the kidney.

CLINICAL DISCUSSION

Although this tumor is rare, we need to keep it in mind as a potential diagnosis for renal lesions in our clinical practice.

CONCLUSION

The presence of a low-grade malignancy and metastasis in this tumor is a good sign, and this is what motivates us to obtain more reports to better understand the nature of this tumor formation, which is important for human health.

[Thyroid-like follicular carcinoma of the kidney]

Thyroid-like follicular carcinoma of the kidney (TLFCK) is an extremely rare histological variant of renal cell carcinoma, not yet included in the WHO list of tumors. This tumor has a characteristic morphological structure strikingly resembling follicular carcinoma of the thyroid gland, but differing from itby the immunophenotype of tumor cells. TLFCK is characterized by an indolent clinical course, rarely metastases, and even the presence of metastases does not lead to a worsening of the prognosis for the patient. Described a case of TLFCK diagnosed in a 38-year-old patient, observed clinically for 8 years, without metastases during this time, and removed by focal kidney resection. The paper presents the macroscopic and microscopic characteristics of the tumor, immunohistochemical profile, and discusses the issues of differential diagnosis.

[Rare kidney tumor - thyroid-like follicular carcinoma]

The literature review provides an analysis of a rare malignant tumor of the kidney: thyroid-like follicular carcinoma of the kidney (TLFCK). In morphology, this tumor is extremely similar to thyroid follicular carcinoma, but the immunophenotype of tumor cells is different. TLFCK has an indolent clinical course, rarely metastasizes, and even the development of metastases does not mean an unfavorable prognosis for the patient. The literature review presents the features of the clinical course of the disease, macroscopic, microscopic, immunohistochemical characteristics of the tumor and typical cytogenetic breakdowns. Particular attention is paid to the issues of differential diagnosis of the tumor with other pathological processes that may microscopically resemble TLFCK.

EWSR1-PATZ1 fusion renal cell carcinoma: a recurrent gene fusion characterizing thyroid-like follicular renal cell carcinoma

Thyroid-like follicular renal cell carcinoma is an uncommon kidney tumor with no distinct molecular alteration described to date. This cohort of eight women with mean and median ages of 45 and 46 years, respectively (range 19-65 years), had unencapsulated, well-circumscribed tumors composed of tightly packed anastomosing follicle-like cysts filled with eosinophilic colloid-like material and lined by cuboidal cells with high nuclear to cytoplasmic ratios, oval to elongated nuclei with perpendicular arrangement toward the lumens, and prominent nuclear overlapping. The stroma between these was minimal with the exception of two tumors. Calcifications and necrosis were absent. Immunohistochemically, the tumors were positive for KRT19 (7/7), PAX8 (5/5), cyclin D1 (6/6), KRT7 (5/7), and AMACR (1/5; focal, weak), and were negative for WT1, TTF1 (transcription termination factor-1), and thyroglobulin. In three of three tumors tested molecularly, EWSR1-PATZ1 fusion was identified by RNA sequencing and confirmed by RT-PCR and Sanger sequencing. Over a follow-up period of 1-7 years, no evidence of recurrence or metastasis has been detected. The EWSR1-PATZ1 fusion has been recognized as a recurrent alteration in a subset of round to spindle cell sarcomas with EWSR1-non-ETS fusions (EWSR1-PATZ1 sarcoma) and in several central nervous system tumors. The finding of an EWSR1-PATZ1 fusion in all three of the thyroid-like follicular renal cell carcinomas for which sufficient tissue was available for genomic profiling provides the first distinct molecular abnormality in thyroid-like follicular renal cell carcinomas, supporting its designation as a distinct diagnostic entity.

Thyroid-Like Follicular Carcinoma of the Kidney With Low-Grade Sarcomatoid Component: A Hitherto Undescribed Case

Thyroid-like follicular carcinoma of the kidney (TLFCK) is a rare subtype of renal cell carcinoma, which closely resembles follicular neoplasms of the thyroid and has a distinctive indolent clinical behavior. Until now, a single case of TLFCK with extensive sarcomatoid differentiation has been documented with aggressive clinical course. We present an unusual case of sarcomatoid TLFCK with a low-grade spindle cell component in a 34-year-old male patient, with an indolent course following radical nephrectomy and regional node dissection.

Thyroid-like follicular carcinoma of the kidney presenting on a 10 year-old prepubertal girl

The very rare thyroid-like carcinoma of the kidney (TLCK) is microscopically similar to thyroid follicular cell carcinoma (TFCC). Differential diagnosis with secondary thyroid tumors depends on non-reactivity to immunohistochemical (IHC) markers for TFCC (thyroglobulin - TG and TTF1). We herein describe the fourth Pediatric case in literature and extensively review the subject. Only 29 cases were published to the moment. Most cases were asymptomatic and incidentally detected. Most tumors are hyperechoic and hyperdense with low grade heterogenous enhancement on CT and MRI. Most patients were treated with radical nephrectomy, but partial nephrectomy was used in some cases, apparently with the same results. Metastases are uncommon and apparently do not change prognosis, but follow-ups are limited. Up to the moment, TLCK presents as a low grade malignancy that may be treated exclusively with surgery and frequently with partial kidney renal preservation. A preoperative percutaneous biopsy is a common procedure to investigate atypical tumors in childhood and adult tumors. To recognize the possibility of TLCK is fundamental to avoid unnecessary thyroidectomies in those patients, supposing a primary thyroid tumor.

Thyroid follicular carcinoma-like renal tumor: A case report and literature review

RATIONALE

Thyroid follicular carcinoma-like renal tumor (TFCLRT) is a rare primary renal epithelial tumor that was first reported in 2006. We report a case diagnosed of TFCLRT by us to observe the pathological feature and analyze comparatively the clinical and pathologic characteristics with all cases of reviewed literatures.

PATIENT CONCERNS

A 54-year-old female patient had the urinary frequency with the symptom of right flank pain with a history of more than half a year of hypertension and received uterine fibroid resection 12 years ago. B-mode ultrasound examination and renal magnetic resonance showed a right renal sinus nodule.

DIAGNOSES

Histopathology revealed thyroid follicle-like structures of different sizes, containing a colloid-like substance, while the periodic acid-Schiff (PAS) and diastase-resistant PAS staining confirmed that it was mucus protein. Immunohistochemical staining showed that it expresses the transcription factor PAX-8 but does not express the thyroid-specific antibodies TG and TTF-1.

INTERVENTIONS

The patient underwent a tumor enucleation of right kidney. No other treatment was conducted after surgery.

OUTCOMES

No metastases to lymph nodes and other organs were found, and 9-months of follow-up did not reveal any tumor progression.

LESSONS

We should differentially diagnose the renal metastasis of thyroid follicular carcinoma or papillary carcinoma. Some related literatures reported that the tumour cells had significant heteromorphism, several of which metastasized to lymph nodes or distal organs. Its biological behavior need to be studied intensively by further expanding the number of cases.

Clinicopathological study on thyroid follicular carcinoma-like renal tumor related to serious hypertension: Case report and review of the literature

RATIONALE

Thyroid carcinoma-like tumor of the kidney (TLFCK) is an extremely rare variant of renal cell carcinoma. Most cases were incidentally found, while we report the first case of TLFCK presented with hypertension.

PATIENT CONCERNS

A 25-year-old woman was admitted to our hospital presenting with hypertension for ∼20 months, without gross hematuria, weight loss, and flank pain.

DIAGNOSES

Imaging studies revealed a right renal mass with multiple calcifications. Histologically, the tumor had striking follicles with dense, colloid-like material resembling thyroid follicular carcinoma while the tumor cells were negative for thyroid markers (thyroglobulin and thyroid transcription factor-1).

INTERVENTIONS

The patient successfully underwent nephron sparing surgery with an uneventful recovery.

OUTCOMES

Hypertension returned to normal without any medication interference. Two years after surgery, the patient is still in good health without recurring disease or related hypertension.

LESSONS

Recognition of the cytomorphological features of TLFCK can avoid misdiagnosis of this renal tumor as a metastatic carcinoma and the objective of surgical management is to remove the tumor and preserve renal function.

Molecular genetics and immunohistochemistry characterization of uncommon and recently described renal cell carcinomas

Renal cell carcinoma (RCC) compromises multiple types and has been emerging dramatically over the recent several decades. Advances and consensus have been achieved targeting common RCCs, such as clear cell carcinoma, papillary RCC and chromophobe RCC. Nevertheless, little is known on the characteristics of several newly-identified RCCs, including clear cell (tubulo) papillary RCC, Xp11 translocation RCC, t(6;11) RCC, succinate dehydrogenase (SDH)-deficient RCC, acquired cystic disease-associated RCC, hereditary leiomyomatosis RCC syndrome-associated RCC, ALK translocation RCC, thyroid-like follicular RCC, tubulocystic RCC and hybrid oncocytic/chromophobe tumors (HOCT). In current review, we will collect available literature of these newly-described RCCs, analyze their clinical pathologic characteristics, discuss their morphologic and immunohistologic features, and finally summarize their molecular and genetic evidences. We expect this review would be beneficial for the understanding of RCCs, and eventually promote clinical management strategies.

Thyroid-Like Follicular Carcinoma of the Kidney in a Patient with Skull and Meningeal Metastasis: A Unique Case Report and Review of the Literature

Thyroid-like follicular carcinoma of the kidney (TLFCK) is an extremely rare subtype of renal cell carcinoma with close resemblance to the well-differentiated thyroid follicular neoplasms. TLFCK has not been included in the 2004 World Health Organization (WHO) classification due to the limited data available. Only 27 cases have been reported in the literature to date. Herein, we report a unique case of TLFCK that presented as a striking skull and meningeal metastasis 5 years after the initial diagnosis; this is the first case of TLFCK with such a novel metastasis pattern. A 68-year-old woman was found to have a right renal lesion using computed tomography (CT) during her regular clinical follow-up visit for bladder cancer, but she exhibited no obvious clinical symptoms. The CT scan showed a 4.4-cm diameter, slightly lobulated soft tissue mass in the right lower kidney, the pathological findings of which showed a TLFCK. Five years later, the patient had progressed to skull and meningeal metastasis. Both the renal tumor and the metastasis lesion were composed almost entirely of follicles with a dense, colloid-like material that resembled thyroid follicular carcinoma. However, no lesion was found in the thyroid gland. The neoplastic epithelial cells were strongly immunoreactive for cytokeratin 7 (and vimentin but negative for thyroid transcription factor-1 and thyroglobulin. This is the first reported case of TLFCK to consist of widespread metastases to the skull and meninges and provides evidence that this rare variant of renal cell carcinoma has uncertain malignant potential and can be more clinically aggressive than previously believed.

Clinical characteristics and pathology of thyroid-like follicular carcinoma of the kidney: Report of 3 cases and a literature review

Thyroid-like follicular carcinoma (TLFC) of the kidney is an extremely rare type of renal tumor, which has not been classified under a known subtype of renal cell carcinoma. It is histologically similar to the primary thyroid follicular carcinoma; however, the characteristics lack thyroid immunohistochemical markers. The aim of the present study was to illustrate the clinical characteristics of 3 new cases along with a review of the literature. The patients were compared with regards to gender, age, location and size of the tumor, imageology, morphology, immunohistochemistry and prognosis. According to the limited data, TLFC occurs mainly in young women and its clinical manifestations have no difference with other renal tumors. Its imageological features resemble a large spectrum of benign and malignant renal and extra-renal conditions, which should be eliminated in the diagnostic process. Confirmed diagnosis depends on the examination of pathology and immunohistochemistry. Surgical ablation is the preferred therapeutic method. Currently, TLFC has a relatively good prognosis; however, this conclusion requires further cases and long-term follow-ups. Improving the understanding of TLFC can help avoid misdiagnosis and prevent inappropriate treatment.

Thyroid-like follicular carcinoma of the kidney: one case report and review of the literature

OBJECTIVES

Thyroid-like follicular carcinoma of the kidney continues to confound the practicing pathologist with its close resemblance to the follicular variant of thyroid carcinoma, as well as other benign and malignant entities. Our goal is to expand the knowledge of this rare renal cell carcinoma subtype, which is morphologically similar to follicular carcinoma of the thyroid but lacks expression of characteristic thyroid immunohistochemical markers such as TTF-1 and thyroglobulin.

METHODS

We evaluated the gross, histologic, immunohistochemical, and fluorescence in situ hybridization (FISH) studies of a new case and performed a comprehensive review of the literature.

RESULTS

The lesion was spongy and well-circumscribed. Microscopically it showed variably sized follicular structures, filled with abundant, deeply eosinophilic, colloid-like material. At the periphery, it displayed areas resembling metanephric adenoma and early stages of nephrogenesis. The tumor cells strongly expressed CK7, PAX-8, PAX-2, vimentin, EMA, and CK19 immunostains. Other markers, such as CD10, RCC, HBME-1, thyroglobulin, and TTF-1, were not immunoreactive. The tumor was negative for trisomy of both 7 and 17 and showed borderline monosomies (losses) of both chromosomes in FISH studies.

CONCLUSIONS

Five years of preoperative observation and lack of recurrence bring further insight into the slow progressive nature of this neoplasm and support a low malignant potential. Proper identification is important to secure adequate treatment and follow-up.

Diagnostic approach to eosinophilic renal neoplasms

CONTEXT

Eosinophilic renal neoplasms include a spectrum of solid and papillary tumors ranging from indolent benign oncocytoma to highly aggressive malignancies. Recognition of the correct nature of the tumor, especially in biopsy specimens, is paramount for patient management.

OBJECTIVE

To review the diagnostic approach to eosinophilic renal neoplasms with light microscopy and ancillary techniques.

DATA SOURCES

Review of the published literature and personal experience.

CONCLUSIONS

The following tumors are in the differential diagnosis of oncocytic renal cell neoplasm: oncocytoma, chromophobe renal cell carcinoma (RCC), hybrid tumor, tubulocystic carcinoma, papillary RCC, clear cell RCC with predominant eosinophilic cell morphology, follicular thyroid-like RCC, hereditary leiomyomatosis-associated RCC, acquired cystic disease-associated RCC, rhabdoid RCC, microphthalmia transcription factor translocation RCC, epithelioid angiomyolipoma, and unclassified RCC. In low-grade nonpapillary eosinophilic neoplasms, distinction between oncocytoma and low-grade RCC mostly rests on histomorphology; however, cytokeratin 7 immunostain may be helpful. In high-grade nonpapillary lesions, there is more of a role for ancillary techniques, including immunohistochemistry for cytokeratin 7, CA9, CD10, racemase, HMB45, and Melan-A. In papillary eosinophilic neoplasms, it is important to distinguish sporadic type 2 papillary RCC from microphthalmia transcription factor translocation and hereditary leiomyomatosis-associated RCC. Histologic and cytologic features along with immunohistochemistry and fluorescence in situ hybridization tests for TFE3 (Xp11.2) and TFEB [t(6;11)] are reliable confirmatory tests. Eosinophilic epithelial neoplasms with architecture, cytology, and/or immunoprofile not qualifying for either of the established types of RCC should be classified as unclassified eosinophilic RCC and arbitrarily assigned a grade (low or high).

Thyroid-like follicular carcinoma of the kidney: a case report and review of the literature

Thyroid-like follicular carcinoma of the kidney is an extremely rare histological variant of renal cell carcinoma. It was described only recently and is not included in the World Health Organization classification of renal tumors. This tumor characteristically shows similar histology to thyroid follicular carcinoma but lacks typical thyroid markers. Herein, we report a new case of thyroid-like follicular carcinoma of the kidney diagnosed in a partial nephrectomy specimen in a 68-year-old-woman. We present typical histological and immunohistochemical findings, discuss differential diagnosis and provide a review of the literature.

Virtual Slides: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_186

Thyroid-like follicular carcinoma of the kidney in a young patient with history of pediatric acute lymphoblastic leukemia

Thyroid-like follicular carcinoma of the kidney (TLFCK) is a rare histological variant of renal cell carcinoma not currently included in the World Health Organization classification of renal tumors. Only 24 previous cases of TLFCK have been reported to date. We report a case of TLFCK in a 19-year-old woman with history of pediatric acute lymphoblastic leukemia. This patient is the youngest with TLFCK to be reported to date and the first with history of lymphoblastic leukemia. The development of TLFCK in a young patient with history of lymphoblastic leukemia is interesting and suggests that genes involved in leukemogenesis may also be important for TLFCK pathogenesis. Recognition of TLFCK is important to distinguish it from other conditions that show thyroid-like features, as a misdiagnosis can result in adverse patient care.

Thyroid-like follicular carcinoma of the kidney: A report of two cases and literature review

There have only been a few reports of thyroid-like follicular carcinoma of the kidney (TLFCK) to date. In the present study, two patients with TLFCK are reported. Patient 1 was a 65-year-old male exhibiting repeated hematuria and right back pain. No tumors were located in the patient's thyroid or lungs. The physical examination revealed percussion tenderness over the right kidney region was noticed. Enhanced computed tomography (CT) indicated a right renal pelvic carcinoma, for which the patient underwent a radical right nephrectomy. Patient 2 was a 59-year-old male with a mass in the right kidney, located during a health examination and who exhibited no obvious clinical symptoms. The patient was clinically diagnosed with right renal carcinoma, confirmed by an enhanced CT. The patient underwent a radical right nephrectomy. The clinical features, imaging results, pathology, immune phenotypes, treatment and prognosis were analyzed. The associated literature was also reviewed. The cut surface of each tumor showed gray-white material with a central solid area, including scattered gray-brown necrotic and gray hemorrhagic areas and small cystic cavities. Microscopically, the arrangement of the tumor cells mimicked thyroid follicles with red-stained colloid-like material in the lumen. No renal hilar lymph node involvement was noted. The tumor tissue of patient 1 was immunohistochemically positive for vimentin, epithelial membrane antigen (EMA), cytokeratin (CK), CK7, and neuron specific enolase; and negative for CK34BE12, synapsin (Syn), CK20, cluster of differentiation 56 (CD56), CD10, Wilm's tumor-1 (WT-1), CD34, CD57, P53, CD99, thyroid transcription factor-1 (TTF-1), CD15 and thyroglobulin (TG); with a Ki-67 labeling index (LI) of 30%. The tumor tissue of patient 2 was immunohistochemically positive for vimentin, EMA, CK7 and CK20; and negative for CD56, CD10, WT-1, CD34, CD57, P53, CD117, TTF-1, CD15, CD99, TG, chromogranin A and Syn; with a Ki-67 LI of 20%. TLFCK is a rare renal tumor with low malignancy but medium invasiveness. It morphologically resembles thyroid follicular carcinoma but does not express TTF-1 or TG. Radical nephrectomy can achieve good patient outcomes.

Thyroid-like follicular carcinoma of the kidney in a patient with nephrolithiasis and polycystic kidney disease: a case report

Abstract

Thyroid-like follicular carcinoma of the kidney (TLFC), a rare neoplasm with low malignant potential, is histologically similar to primary thyroid follicular carcinoma, but characteristically lacks thyroid immunohistochemical markers. We report a case of 34-year old patient with nephrolithiasis. Ultrasound revealed hepatorenal cysts consistent with adult type polycystic kidney disease (ATPKD) and a cytologically confirmed left kidney tumor. Nephrectomy specimen contained sharply demarcated lesion of unusual morphology. Tubular and cystic structures lined by mostly cuboidal cells and filled with amorphous eosinophillic material, reminiscent of follicular carcinoma of the thyroid gland, were diagnostic for TLFC. Thyroid markers were negative. To our knowledge this is the first report of TFLC associated to ATPKD. Brief review of previously published TFLCs, possible relationship between entities and differential diagnosis are discussed.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/8067946569612694

Thyroid-like follicular carcinoma of the kidney: report of two cases with detailed immunohistochemical profile and literature review

Thyroid-like follicular carcinoma of the kidney (TLFC) is an unusual histological variant of renal cell carcinoma not included in the current WHO classification of renal tumors. Its morphological features resemble a large spectrum of benign and malignant renal and extra-renal conditions which should be ruled out in the diagnostic process. Because TLFC outcome is different from the other variants of renal cell carcinoma, the exploration for disease-specific markers is mandatory. The aim of the present paper is to illustrate the histological characteristics and immunohistochemical profile of two new cases along with a brief review of the literature.

Thyroid-like follicular carcinoma of the kidney with metastases to the lungs and retroperitoneal lymph nodes

Thyroid-like follicular carcinoma of the kidney is an extremely rare variant of renal cell carcinoma. Most previously reported cases presented as incidental small tumors confined to the kidney. Here we report a unique case in which the patient presented with flank pain and hematuria. Imaging studies demonstrated a large tumor in the right kidney and metastases to the lungs and retroperitoneal lymph nodes. Both the renal tumor and the sampled lung metastasis were composed almost entirely of follicles with dense, colloid-like material resembling thyroid follicular carcinoma. However, no lesion was found in the thyroid gland; and the patient's thyroid function test results were normal. The tumor cells were immunoreactive for PAX2 and PAX8 but lacked reactivity for thyroglobulin and thyroid transcription factor-1. To our knowledge, this is the first case of thyroid-like follicular carcinoma of the kidney to be initially associated with marked symptoms and widespread metastases, providing evidence that this rare variant of renal cell carcinoma can be clinically aggressive.

Thyroid dysfunction and kidney disease

Thyroid hormones (TH) are essential for an adequate growth and development of the kidney. Conversely, the kidney is not only an organ for metabolism and elimination of TH, but also a target organ of some of the iodothyronines' actions. Thyroid dysfunction causes remarkable changes in glomerular and tubular functions and electrolyte and water homeostasis. Hypothyroidism is accompanied by a decrease in glomerular filtration, hyponatremia, and an alteration of the ability for water excretion. Excessive levels of TH generate an increase in glomerular filtration rate and renal plasma flow. Renal disease, in turn, leads to significant changes in thyroid function. The association of different types of glomerulopathies with both hyper- and hypofunction of the thyroid has been reported. Less frequently, tubulointerstitial disease has been associated with functional thyroid disorders. Nephrotic syndrome is accompanied by changes in the concentrations of TH due primarily to loss of protein in the urine. Acute kidney injury and chronic kidney disease are accompanied by notable effects on the hypothalamus-pituitary-thyroid axis. The secretion of pituitary thyrotropin (TSH) is impaired in uremia. Contrary to other non-thyroidal chronic disease, in uraemic patients it is not unusual to observe the sick euthyroid syndrome with low serum triodothyronine (T(3)) without elevation of reverse T(3) (rT(3)). Some authors have reported associations between thyroid cancer and kidney tumors and each of these organs can develop metastases into the other. Finally, data from recent research suggest that TH, especially T(3), can be considered as a marker for survival in patients with kidney disease.

Primary thyroid-like follicular carcinoma of the kidney: report of 6 cases of a histologically distinctive adult renal epithelial neoplasm

Thyroidization of kidney reminiscent of thyroid follicles with accumulation of inspissated colloid-like material in renal tubules is a hallmark of chronic pyelonephritis. We identified 6 tumors in the kidney, distinct from currently known subtypes of renal cell carcinoma, with a striking histology that closely mimicked well-differentiated thyroid follicular neoplasms and raised the possibility of metastatic follicular thyroid carcinoma. Three occurred in males and 3 in females with an age range of 29 to 83 years and size range from 1.9 to 4 cm. All tumors were encapsulated and exclusively demonstrated follicular architecture comprising of microfollicles and macrofollicles containing inspissated colloid-like material. A minor component of small tightly packed follicles devoid of secretions was also noted. The follicles were lined by cells with moderate amphophilic to eosinophilic cytoplasm with round nuclei and occasional prominent nucleoli. The tumors were nonimmunoreactive with thyroglobulin and thyroid transcription factor 1 and for markers contemporarily used for renal differentiation. The tumors had a gene expression profile distinct from clear cell and chromophobe renal cell carcinoma. Comparative genetic hybridization failed to reveal cytogenetic alterations. Mean follow-up of 47.3 months (range: 7 to 84 mo) showed that 5 patients had no evidence of disease and 1 developed a metastasis to the renal hilar lymph nodes in which the follicular architecture with colloid was retained. Thyroid-like follicular renal cell carcinoma represents a unique histologic subtype of renal cell carcinoma of low malignant potential and its primary importance is to distinguish it from metastatic carcinoma from the thyroid.