C-kit expression in renal oncocytomas and chromophobe renal cell carcinomas

C- kit encodes the membrane-bound tyrosine kinase KIT, whose expression has been identified in several types of human neoplasms. Recently, KIT has been reported to be a marker for chromophobe renal cell carcinoma (RCC) and renal angiomyolipoma. However, expression of this molecule has not been adequately studied in other renal tumors, particularly oncocytoma, which may morphologically resemble chromophobe RCC. In this study, we analyzed c- kit messenger RNA (mRNA) levels in 17 chromophobe RCCs and 20 renal oncocytomas obtained from complementary DNA (cDNA) microarrays. Furthermore, comprehensive immunohistochemical analysis of KIT protein using a monoclonal antibody was performed in 226 renal tumors including chromophobe RCC (n=40), oncocytoma (n=41), clear-cell RCC (n=40), renal angiomyolipoma (n=29), and papillary RCC (n=21) on tissue microarrays (TMAs) and was compared with immunostaining results from 25 chromophobe RCCs and 30 oncocytomas using standard sections. The staining intensity was semiquantitatively graded on a 3-tier scoring system. All chromophobe RCCs and oncocytomas showed significant overexpression of c- kit mRNA. The average increase of mRNA compared with normal kidney tissue was 7.4-fold for chromophobe RCCs and 7.4-fold for oncocytomas. Immunohistochemical expression of KIT was found in most chromophobe RCCs (95% in TMAs and 96% in conventional sections) and oncocytomas (88% in TMAs and 100% in conventional sections) but was infrequently observed in renal angiomyolipomas (17%), papillary RCCs (5%), and clear-cell RCCs (3%). Furthermore, the average KIT immunoreactivity in TMAs was stronger in chromophobe RCC (1.93) and oncocytoma (2.07) than in other subtypes of renal tumors tested, including angiomyolipomas (0.17), papillary RCCs (0.05), and clear-cell RCCs (0.03). In conclusion, we found a significant elevation of c- kit mRNA by cDNA expression microarrays and overexpression of KIT protein by immunohistochemistry not only in chromophobe RCCs but also in oncocytomas. In contrast, immunohistochemical expression of KIT was not detected in most other types of renal cell tumors evaluated. The differential expression of c- kit in these renal tumors may have diagnostic and therapeutic implications.     

Papillary renal cell carcinoma within a renal oncocytoma: case report of an incidental finding of a tumour within a tumour

The most common renal tumours are clear cell, papillary, chromophobe and collecting duct renal cell carcinomas (RCCs), and benign oncocytomas and angiomyolipomas. Tumours with hybrid features between some of these entities have been recognised; in particular, tumours with features of both chromophobe RCC and oncocytoma. Case reports describing one distinct type of primary renal tumour actually within another are very rare. The incidental finding of a papillary RCC located in an oncocytoma in a nephrectomy specimen from a 75-year-old man is described. Morphological criteria for each tumour type were completely satisfied and fluorescence in situ hybridisation detected the expected number of copies of chromosome 7 in the cells of each tumour type. The cells in the papillary tumour contained three copies, whereas the oncocytoma cells contained only two per nucleus. To our knowledge, this is the first report of a papillary RCC being identified within an oncocytoma.     

Triple synchronous neoplasms in one kidney: report of a case and review of the literature

We report the case of a patient with three synchronous but histologically different primary renal tumors that were all in the same kidney. Two tumors were different subtypes of renal cell carcinoma (RCC), and the third was a variant form of angiomyolipoma. The patient was a 62-year-old man who was receiving antihypertensive drugs and came to our hospital for a regular check-up. Ultrasonography performed during the visit revealed a left renal mass, but the patient had no related symptoms. Subsequent computed tomography revealed two round, high-density masses, one in the mid-portion and the other in the lower pole of the left kidney, and multiple cysts in the right kidney and the liver. The mass in the mid-portion measured 3.3 x 3.0 x 2.8 cm, and the mass in the lower pole measured 1.7 x 1.1 x 0.9 cm. A left radical nephrectomy was performed. On gross examination, an additional ovoid nodule (0.6 cm in the greatest dimension) was found in the lower pole. Microscopically, the largest tumor consisted of a broad alveolar arrangement of large round cells with abundant eosinophilic or clear cytoplasm, distinct cell borders, and perinuclear halos, features consistent with chromophobe RCC. The smallest tumor was a conventional (clear-cell) RCC. The third tumor was composed solely of atypical epithelioid cells with prominent nucleoli and yellowish-brown to black pigments. The tumor cells were positive for melanin (Fontana-Masson stain), the melanoma marker HMB45, vimentin, smooth-muscle actin, and the macrophage marker CD68 and were negative for cytokeratin. This tumor was considered a pigmented epithelioid type of angiomyolipoma. The histologic, histochemical, and immunohistochemical features in this case confirmed the presence of three synchronous primary tumors, a chromophobe and a clear-cell type RCC and a pigmented epithelioid angiomyolipoma, all of which were in the same kidney. This case is the first of its type reported in the literature.     

Clinical features of renal cell carcinoma (RCC) found in 110 nephrectomized Japanese, of which 24 (22%) RCC cases showed 31 double or triple cancers

The causes of renal cell carcinoma (RCC) were investigated in 115 nephrectomized Japanese. Among them, 110 nephrectomized Japanese had RCC as follows: 86 clear cell RCC, 8 papillary RCC, 8 chromophobe RCC, 7 dialytic–multicystic RCC, and 1 liposarcoma, while 5 nephrectomized Japanese had benign renal tumors of oncocytoma (1), angiomyolipoma (2), and hemangioma (2). In the eight chromophobe RCC, three cases that resulted in death involved medullary RCC showing extensive oncogenic features. Double or triple cancers were found in 17 clear cell RCC, 5 papillary RCC, 1 chromophobe RCC, and 1 dialytic–multicystic RCC. Among 31 non-RCC found in 24 RCC cases, 23(74%) non-RCC were removed prenephrectomy. Prenephrectomy adenocarcinoma and postnephrectomy squamous cell carcinoma were their characteristic findings. Compared with those of clear cell RCC, double (triple) cancers of papillary RCC showed more aggressive malignancy. One clear cell RCC had triple cancer of thymoma and rectum cancer. One chromophobe RCC developed thymoma, while one oncocytoma had insulinoma >10 years before. A patient in his sixties with clear cell RCC, who had a past history of pneumothorax, had developed adenocarcinoma of colon polyps and liver adenocarcinoma almost at the same time as triple cancer. His lactate dehydrogenase (LDH) levels were under 300 IU/l. He was suspected of having Birt–Hogg–Dube syndrome. One patient with papillary RCC of Paget’s disease of the bone developed colon polyp adenocarcinoma, osteosarcoma, and additionally exhibited p97/valosin-containing protein downregulation in his sixties. His LHD was increased to 4,289 IU/l with cell lysis reactions. His radical nephrectomy accompanied by adrenalectomy reinforced clinical manifestations of p97 downregulation. For p97 functions, the kidney and adrenal gland had important roles. It was concluded that oxygen stress was stronger in RCC, especially in papillary RCC. Nonsense mutations of protein tyrosine phosphatase receptor delta might be one cause of double (triple) cancers in RCC.     

Carbonic anhydrase IX expression in renal neoplasms: correlation with tumor type and grade

Carbonic anhydrase IX (CAIX), a hypoxia-induced protein, is expressed in some renal tumors. We evaluated its immunohistochemical expression in 317 primary and 42 metastatic renal neoplasms (186 clear cell, 52 papillary, 35 chromophobe, 47 unclassified, and 15 Xp11.2 translocation renal cell carcinomas [RCCs]; 26 oncocytomas; 2 metanephric adenomas; 1 urothelial carcinoma; 1 mixed epithelial and stromal tumor; and 1 angiomyolipoma); 7 neoplasms were unknown as to whether they were primary or metastatic. We also correlated expression with tumor type and grade. Variable staining was seen in clear cell, papillary, unclassified, and Xp11.2 translocation carcinomas. One chromophobe carcinoma had focal expression. No staining was seen with other tumors. An association was found between high expression and clear cell vs non-clear cell carcinomas with all cases (P < .01) and primary (P < .01) cases. An association between CAIX expression and grade (P < .01) in primary clear cell carcinomas was found. CAIX expression is more common in clear cell RCC than other renal tumor types and is associated with grade.     

Alpha-methylacyl-CoA racemase as a marker in the differential diagnosis of metanephric adenoma.

Metanephric adenoma (MA), a well-described renal neoplasm, usually behaves in a benign fashion. It may have areas that are morphologically similar to papillary renal cell carcinoma (RCC) type, or epithelial (tubular predominant) type Wilms' tumor. Prior immunohistochemical studies of MA have reported variable staining patterns. Alpha-methylacyl-CoA racemase (AMACR), a molecular marker for prostate carcinoma, has subsequently been found to be overexpressed in breast, colorectal and ovarian cancers, among others. Recent microarray analysis of renal tumors has shown an increase of AMACR mRNA levels in papillary RCC but not in other subtypes. We investigated the utility of immunohistochemical staining for AMACR, cytokeratin 7(CK7), CD57 and WT1 to differentiate between the above-mentioned three neoplasms. Immunohistochemical stains were performed on paraffin-embedded tissue sections from 25 papillary RCC, 10 MAs and eight Wilms' tumors. AMACR was positive in one (10%) of 10 MAs and 24 (96%) of 25 papillary RCC, while it was negative in all Wilms' tumors. CK7 was positive in 20 of 25 papillary RCCs, focally positive in one Wilms' tumor and was negative in all MAs. CD57 was positive in all six MAs that were stained, focally positive in one of 25 papillary RCC and one of eight Wilms' tumors. WT1 was positive in seven of 10 MAs, three of 25 papillary RCCs and all eight Wilms' tumors. In conclusion, diffuse and strong immunoreactivity for AMACR may be useful in differentiating papillary RCC from MA but a panel which includes AMACR, CK7 and CD57 is better in this differential diagnosis. AMACR is not helpful in differentiating MA from Wilms' tumor, but CD57 is helpful in this differential diagnosis. WT1 may be useful in separating Wilms' tumor from MA and papillary RCC but is not helpful in differentiating MA from papillary RCC.     

Clear cell papillary renal cell carcinoma and clear cell renal cell carcinoma arising in acquired cystic disease of the kidney: an immunohistochemical and genetic study

Clear cell papillary renal cell carcinoma (RCC) is a recently established disease entity. However, there are few reports on genetic study of this entity. We report such a case with focus on genetic study. A 57-year-old Japanese man was found to have 3 renal tumors. Histologically, two tumors showed findings of clear cell RCC; and the other tumor showed findings of clear cell papillary RCC that was characterized by papillary growth pattern of neoplastic cells in cystic space with purely clear cell cytology. Immunohistochemically, tumor cells of clear cell papillary RCC were diffusely positive for PAX2 and cytokeratin 7, but negative for CD10, RCC Ma, and AMACR. In fluorescence in situ hybridization study for one clear cell papillary RCC, we detected polysomy for chromosome 7 and monosomy for chromosomes 17, 16, and 20. In addition, we detected mutation of VHL gene in clear cell RCC, but found no VHL gene mutation in clear cell papillary RCC. Finally, our results provide further evidence that clear cell papillary RCC may be both morphologically and genetically distinct entity from clear cell RCC and papillary RCC.     

Spectrum of renal pathology in adult patients with congenital renal anomalies—a series from a tertiary cancer center

Congenital renal anomalies (CRAs) detected in adults include horseshoe kidney (HK), crossed renal ectopia, and malrotation. Congenital renal anomalies are rare, and renal lesions associated with CRA are rarer. Thirteen patients (11 men and 2 women) were referred to our center with renal masses in the context of CRAs, which included HK (10 cases), crossed renal ectopia (2 cases), and a pelvic kidney (1 case). The mean age at diagnosis was 60 years (37-76 years). All patients were treated with open surgery; 10, partial nephrectomies; 4, radical nephrectomies; and 1, nephroureterectomy with division of the renal isthmus. Pathology ranged from benign (simple cortical cysts, chronic pyelonephritis with secondary hydronephrosis) to malignant (12 cases of renal cell carcinomas [RCCs] and 1 case of urothelial carcinoma). Two patients of HKs presented with bilateral renal masses. The size of the RCC ranged from 2.5 to 13 cm. There were 11 cases of clear cell RCC, 1 case of papillary RCC (type 1), and 1 case of urothelial carcinoma. All the cases of RCC had negative surgical margins. Follow-up available in all patients ranged from 1 month up to 49 months. None of the patients developed any locoregional recurrences or distant metastases. In this patient cohort, the most common congenital anomaly associated with RCC is HK. All tumors behaved in an indolent fashion with prognosis related to pathologic tumor stage. Partial nephrectomy is a safe and effective procedure in appropriately selected patients.     

Acquired cystic disease-associated renal cell carcinoma with gain of chromosomes 3, 7, and 16, gain of chromosome X, and loss of chromosome Y

Acquired cystic disease (ACD)-associated renal cell carcinoma (RCC) has been recently described. To date, there are no reports on genetic findings of G-band karyotype of ACD-associated RCC. In this article, we report the first report of G-band karyotype of ACD-associated RCC. A 66-year-old Japanese man was found to have a left renal tumor during the follow-up of hemodialysis consequent to chronic renal failure. Left nephrectomy was performed. Histological examination of three tumors in the left kidney showed the cribriform or microcystic growth pattern of neoplastic cells with eosinophilic cytoplasm, and many oxalate crystals were observed. The G-band karyotype of ACD-associated RCC showed 49, X, +X, −Y, +3, +7, +16. These chromosomal abnormalities resemble those of sporadic papillary RCC that has been previously reported. Finally, we suggest that this tumor may show a close relationship between ACD-associated RCC and papillary RCC, but a large-scale study will be needed to clarify the relationship between ACD-associated RCC and papillary RCC.     

Association of cystic nephroma with angiomyolipoma in the same kidney

The synchronous occurrence of two different renal tumors in a patient is a rare event. Here we report an incidentally discovered coexistence of cystic nephroma with angiomyolipoma in the right kidney. The patient was a 68-year-old woman without the tuberous sclerosis complex. To the best of our knowledge, this combination of neoplasms has not yet been described before. This rare situation emphasizes the need for careful diagnosis and the correct management of coincident renal neoplasms.     

Tumor-to-tumor metastasis: report of 2 cases of metastatic carcinoma to angiomyolipoma of the kidney

Tumor-to-tumor metastasis is a rare phenomenon. Renal cell carcinoma is the most common recipient of tumor-to-tumor metastasis in malignant tumors. However, renal angiomyolipoma has not been reported to be a recipient. Here we report 2 cases of tumor-to-tumor metastasis to renal angiomyolipoma. In one case, the donor tumor originated from neuroendocrine carcinoma of the pancreas, and in the other case the donor tumor was from adenocarcinoma of the lung. The donor tumors showed morphologic features that did not easily fit into renal angiomyolipoma, and they also demonstrated patterns of immunoreactivity consistent with the primary tumors rather than with renal angiomyolipoma. To our knowledge, these are the first reported cases of tumor-to-tumor metastasis to renal angiomyolipoma. An awareness of this phenomenon is important to avoid an incorrect diagnosis when encountering unusual morphologic features in renal angiomyolipoma.     

Epithelioid angiomyolipoma of the kidney: case report

Renal angiomyolipoma is a benign tumour histologically characterized by a mixture of adipose tissue, smooth muscle cells and thick walled blood vessels. Long-believed to be a benign hamartoma, angiomyolipoma is now considered to arise from perivascular epithelioid cells. Epithelioid angiomyolipoma is a rare type of angiomyolipoma, composed partially or completely of epithelioid cells, with a potentially aggressive behaviour. Histologically it can mimic renal cell carcinoma. Positivity for HMB45, Melan A, CD68 and CD117 are useful for diagnosis. Herein, we report the clinicopathologic and immunohistochemical features of a renal tumour composed of large epithelioid mononucleated or multinucleated cells with abundant acidophilic cytoplasm and prominent nucleoli. Despite the morphologic resemblance of this tumour to renal cell carcinoma, its phenotype (HMB45, Melan A and CD68 positivity and keratin negativity) parallels the phenotypic profile of angiomyolipoma. Therefore, immunohistochemistry should be considered when diagnosing this variant of angiomyolipoma.     

Renal angiomyoadenomatous tumor

We report a case of a 40-year-old woman with renal angiomyoadenomatous tumor, a rare neoplasm with only 6 previous cases reported in the literature. Unlike our case, most tumors have been identified in middle-aged males; they present as well-circumscribed, encapsulated tan-brown masses with variably prominent cystic areas. Microscopically, the tumors have a variably thick leiomyomatous capsule, which invaginates into the tumor and intermixes with tubules or solid nests of clear epithelial cells. The epithelial cells have low-grade basally oriented nuclei, and their basement membranes are intimately linked to a labyrinthine network of capillaries and pericytes. Microscopically, these tumors can be confused with clear cell carcinoma, papillary carcinoma, mixed epithelial and stromal tumors, and angiomyolipoma. This is also the first case report correlating the radiographic and morphological findings of this rare entity. The differentiating features of these neoplasms and a review of literature of are herein presented.     

Immunohistochemical application of S100A1 in renal oncocytoma, oncocytic papillary renal cell carcinoma, and two variants of chromophobe renal cell carcinoma

S100A1 is a calcium-binding protein and a member of the S100 family. Recently, S100A1 immunohistochemistry may be an available marker in the differential diagnosis between renal oncocytoma and chromophobe renal cell carcinoma (RCC). However, there are no reports on S100A1 expression in oncocytic papillary RCC that has been recently identified. In this article, we immunohistochemically examined the expression of S100A1 protein in 18 renal tumors including 4 renal oncocytoma, 10 chromophobe RCCs, and 4 oncocytic papillary RCCs. All the cases of renal oncocytoma and oncocytic papillary RCC showed a positive reaction for S100A1 with cytoplasmic pattern. In chromophobe RCC, 3 of 4 tumors with typical variant and 4 of 6 tumors in eosinophilic variant were completely negative for S100A1. Finally, S100A1 immunohistochemistry may be useful in distinguishing renal oncocytoma from chromophobe RCC, but it may be of no use in the differential diagnosis between renal oncocytoma and oncocytic papillary RCC.     

Primary collision tumors of the kidney composed of oncocytoma and papillary renal cell carcinoma: A review

BackgroundThere are well known cases of hybrid tumors of chromophobe renal cell carcinoma (RCC) and oncocytoma in kidney, where both tumors have the same cell of origin – intercalated cell of the collecting duct. However, collision tumors composed of neoplasms originating from different cell lineages such as oncocytoma and papillary RCC are extremely rare. Herein, we made a collective literature review of reported cases of collision tumors composed of oncocytoma and papillary RCC, adding a case that we recently experienced.Material and methodsA PubMed database was search for collision tumors of the kidney composed of oncocytoma and papillary RCC and a collective literature review was made. To this cohort, we also added a recently encountered case with similar, confirmed by immunohistochemistry, morphological features.ResultsTo date 8 cases of a collision tumor composed of papillary RCC and oncocytoma have been described in the literature. All of them had a smaller papillary RCC component present within a larger oncocytoma.ConclusionBecause of a few cases of such a collision tumors reported, it is difficult to make classification and right clinical management of these patients. None of the reported cases had tumor recurrence or progression on a follow-up. The presence of only small portion of papillary RCC in a large oncocytoma raises a possibility of under-sampling of malignant component in large oncocytomas in core biopsy or surgically resected specimens. We recommend better sampling, particularly at the periphery of otherwise classic oncocytomas to unveil this possible association.     

Papillary cystadenoma of the epididymis. Case report and review of the literature

The only known benign epithelial tumor of the epididymis is papillary cystadenoma. Since 1921, only 39 such tumors have been published. We report on a papillary cystadenoma in a 30-year-old patient. The tumor measures 1.5 cm and is located in the head of the left epididymis. Histomorphologically, these tumors are characterized by cysts with colloid-like contents and papillary formations of light epithelium. Papillary cystadenoma can occur uni- or bilaterally, most frequently in the head of the epididymis. Age of patients ranges between 16 and 81 years with 36.6 years on average. Bilateral papillary cystadenomas are combined in 65, unilateral in 18% with Hippel-Lindau' disease. Most authors regard ductuli efferents as point of origin of these rare benign tumors.     

Urothelial (transitional cell) papilloma of the urinary bladder: a clinicopathologic study of 26 cases.

The existence of a papillary lesion of the urinary bladder with a benign clinical course and recognizable morphologic features that merit the benign categorization "papilloma" has been controversial. The clinical aspects and histologic features of these lesions remain to be fully elucidated. We have studied the clinicopathologic features of 26 patients with urothelial papillomas and correlated them with outcome. Papillomas occurred in two distinct clinical settings: (1) de novo neoplasms (23/26) or (2) those occurring in patients with a known clinical history of bladder cancer ("secondary" papillomas; 3/26). Follow-up information was available in 14/23 of the de novo cases (mean = 39 mo) and in 3/3 secondary cases (mean = 24 mo). Patients with de novo papillomas had a mean age of 46 years; 16 were male and 7 were female. Twelve of 14 had a benign clinical course with no recurrences; 1 developed a recurrent papilloma at 3 years, and 1 developed a pT3a high-grade papillary urothelial carcinoma at 4 years. Patients with secondary papillomas had a mean age of 66 years; two were male and one was a female. One of these patients developed two additional recurrences, and two patients had no new recurrences. Morphologically, the papillary architecture ranged from a common simple, nonhierarchical arrangement to, infrequently, more complex anastomosing papillae with budding. The individual papillae ranged from small (most common), with scant stroma and slender fibrovascular cores, to large, with marked stromal edema and/or cystitis cystica-like urothelial invaginations. Common to all was a lining of normal-appearing urothelium without hyperplasia, maintenance of normal polarity, and frequent prominence of the umbrella cell layer. Overall, no patient with a diagnosis of papilloma died of disease; only one patient with a de novo lesion (7.0%) had a recurrent papilloma, and 1/14 (7.0%) progressed to a higher grade and stage of disease, although this patient was on immunosuppressive therapy secondary to a renal transplant. De novo urothelial papillomas occur in younger patients and usually have a benign course. Urothelial papillomas are histologically and probably biologically distinctive tumors and merit distinction from other higher risk papillary neoplasms of the urinary bladder.     

Renal epithelial neoplasms: the diagnostic implications of electron microscopic study in 55 cases

Several unsettled histogenetic, nosologic and diagnostic considerations for renal epithelial tumors may have ultrastructural ramifications. Yet, a comprehensive electron microscopic study of renal epithelial neoplasms, in light of the recent classification, is not available. The ultrastructural findings from fifty-five renal epithelial neoplasms [31 clear cell renal cell carcinomas (RCC), 11 papillary RCC, 5 chromophobe RCC, 3 sarcomatoid RCC and 5 oncocytomas] were correlated with their light microscopic appearance. Clear cell RCC showed long microvilli similar to the brush border of the normal proximal tubules, with abundant cytoplasmic lipid and glycogen. Papillary RCC showed variably sized microvilli, and small amounts of cytoplasmic lipid, but no glycogen. Chromophobe RCC showed many cytoplasmic vesicles and abnormal mitochondria, with rare short and stubby microvilli. Renal oncocytoma showed many mitochondria with a few vesicles in the apical portion of the cytoplasm and rare short and stubby microvilli. The eosinophilic cell variants of clear cell RCC, papillary RCC and chromophobe RCC showed ultrastructural features similar to those of their respective prototypes, except for an increased numbers of mitochondria in the cytoplasm. One sarcomatoid clear cell RCC showed skeletal muscle differentiation. Two types of cytoplasmic inclusions, i.e. hyaline globules and granules similar to those in the Paneth cells (PC-like granules) were identified only in clear cell RCC, which displayed distinctive ultrastructural features. The current EM study demonstrates distinctive ultrastructural features of renal epithelial neoplasms. The findings lend additional support to the current classification of the pertinent tumor types, facilitate the differential diagnoses, and provide insights into the possible histogenesis of renal epithelial neoplasms.     

Angiomyolipoma of the kidney: expanding disease spectrum demonstrated by 3 cases.

We report 3 recent cases of angiomyolipoma of the kidney. Although generally regarded as a benign neoplasm, angiomyolipoma rarely behaves in an aggressive manner, producing complicated clinical courses leading to metastasis and death. The presence of epithelioid elements within the tumor can result in difficulty differentiating benign from malignant angiomyolipoma and differentiating this tumor from renal adenocarcinoma. The presence of lymph node involvement can cause difficulty in differentiating multicentric disease in lymph nodes from metastasis to lymph nodes. The presence of cytologic abnormalities in the primary tumor can result in difficulty in differentiating atypia in benign angiomyolipoma from malignant sarcomatous transformation of a benign lesion. The 3 cases reported show many of these problems. Criteria for predicting malignancy in epithelioid tumors and sarcomatous transformation are not well recognized because of the rarity of this entity. The typical immunophenotype of all types of angiomyolipoma (cytokeratin-negative and melanomarkers-positive) is very useful in diagnosis but does not help in the differentiation from renal adenocarcinoma at frozen section. We report the empiric use of Ki67 and p53 in these cases as adjuncts to clinical and histologic assessment in predicting behavior. High Ki67 expression was a feature of malignant epithelioid angiomyolipoma. Low levels of p53 expression were seen in the angiomyolipoma with sarcomatous transformation. Benign angiomyolipomas were consistently negative for both Ki67 and p53.