Mixed Epithelial and Stromal Tumor of the Kidney: A Case Report

doi:10.4236/ss.2011.22014

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Surgical Science, 2011, 2, 66-68

doi:10.4236/ss.2011.22014 Published Online April 2011 (http://www.SciRP.org/journal/ss)

Mixed Epithelial and Stromal Tumor of the Kidney:

A Case Report

Ebru Demiralay1, Cem Çomunoğlu1, Handan Özdemir1, Ramazan Yavuz Akman2

1Departmen t o f Pathology, Faculty of Medicine, Baskent University, Ankara, Turkey

2Department of Ur ol o gy, Faculty of Medicine, Baskent Universty, Ankara, Turkey

E-mail: [email protected]

Received December 2, 2010; revised January 25, 2011; accepted Februar y 25, 2011

Abstract

Mixed epithelial and stromal tumor of the kidney (MESTK) is a recently described rare neoplasm. Malignant

transformation, recurrence and metastasis are rare, therefore histopathological distinction from other renal

neoplasms, especially from renal cell carcinoma is important. Histologically the tumor is composed of bi-

phasic components including cysts and tubules embedded in the spindle cell stroma. We report a case of a

MESTK in 60-year-old postmenopousal woman who presented with an incidental solid renal mass but no

urinary complaint.

Keywords: Kidney, Mixed Epithelial and Stromal Tumor

1. Introduction

The mixed epithelial and stromal tumor of the kidney is a

rare and newly defined entity which was included in the

WHO 2004 renal tumor classification [1-7]. To the best

of our knowledge, less than 100 MESTK cases have

been reported. A similar lesion was previously referred

to as cystic hamartoma of the renal pelvis, adult type of

mesoblastic nephroma or cystic nephroma or mature

nephroblastic tumor and cystic partially differentiated

nephroblasto ma [1,4,5,7-10].

Differential diagnosis includes congenital mesoblastic

nephroma, cystic nephroma and multilocular cystic ren al

cell carcinoma [1,4,7,10]. Recent molecular studies sug-

gest that, MESTK has no relationship to mesoblastic

nephroma [8].

Microscopically, the tumor is composed of biphasic

components including cysts and tubules embedded in the

spindle cell stroma. The epithelial elements, composed of

clusters of tubules with variable lining, are found scat-

tered within the spindle cell stroma [2,4-6,8-10]. Cellular

foci reminiscent of ovarian stroma or solitary fibrous

tumor are also present.

Immunohistochemically, desmin, smooth muscle actin

and vimentin are often diffusely and strongly positive in

the spindle cells of the tumors, whereas HMB-45 and CD

34 stains are negative [4,8,10]. Estrogen and progester-

one receptors are frequently positive in the nuclei of the

spindle cells [1,2,4,8,9]. Epithelial elements show usu-

ally positive immunoreactivity with EMA and cy-

tokeratin [1,10].

Although recently a few cases of malignant MESTK

have been reported in the literature, malignant transfor-

mation, recurrence and metastasis are rare.

The aim of this study was to report a case of a MESTK

in 60-year-old postmenopousal woman who presented

with an incidental solid renal mass but without any uri-

nary complaints.

2. Case Report

A 60-year-old postmenopousal woman presented with

cough for 15 days. She had a history of type 2 diabetes

and hyperlipidemia. A computed tomography scan of

thorax showed, as an incidental finding, a solid mass in

right kidney. Contrast enhanced computed tomography

scan of abdomen showed a uniformly lobulated solid

mass with minimal contrast enhancement, situated in the

upper medial aspect of the right kidney, measuring 3.5 ×

3.5 × 3 cm. Neither radiological distinction of malig-

nancy nor exclusion of renal cell carcinoma could be

clearly obtained on magnetic resonance imaging. There

was no evidence of distant metastasis. Physical examina-

tion was unremarkable. She had high glucose level in her

routine blood investigations. Urinary cytological exami-

nation was normal. Radical nephrectomy was performed.

E. DEMIRALAY ET AL.

On gross examination, the tumor was occupying mid

to upper pole of the right kidney. On cut section it had

firm, whitish and solid appearance and it measured 4 × 4 ×

3.5 cm. (Figure 1). The margins of the tumor were sharply

demarcated from the renal parenchyma. No apparent

necrosis or hemorrhage was identified grossly. The renal

parenchyma adjacent to the tumor, renal pelvis, and ure-

ter were unremarkable.

Microscopically, the tumor was composed of biphasic

components including tubules embedded in the spindle

cell stroma (Figure 2). The spindle cell stroma was va-

riably cellular. Cellular foci reminiscent of ovarian stro-

ma were present. Mitotic figures and atypical nuc lei were

absent. The tubules were lined by co lumnar epithelium.

Immunohistochemical examination revealed that the

stromal cells were diffusely positive for smooth muscle

actin, desmin, estrogen receptor and progesterone recep-

tor and negative for HMB-45. The tubular epithelium

was diffusely positive for EMA and pankeratin.

3. Discussion

Mixed epithelial and stromal tumor of the kidney

(MESTK) is a recently described rare neoplasm seen

mostly in adult women [1]. This benign tumor contains

both epithelial and spindle cell stromal components [2].

The term MESTK was first introduced by Michal and

Syrucek in 1998 [1,2,4,5,7-10]. Adsay et al. published

the first large series of this type of tumor with 12 cases

and suggested that MESTK tend to occur in middle aged

and older women. They have reported that the majority

of patients had a history of estrogen therapy [11]. Our

patient who is 60 years old and has been in menopause

for 9 years, had no history of hor monal the rapy.

MESTK are found in adults with a female to male ra-

tio of 10:1. Perimenopausal women in their 5th decade,

with a history of hormonal therapy, are most commonly

affected [1,4,7,10]. In rare reported cases of male pa-

tients, there was a history of hormone therapy [7,9,12].

Common clinical presentations are those of usual renal

mass such as flank pain, hematuria and urinary tract in-

fection or are incidentally diagnosed [2]. MESTK may

mimic renal cell carcinoma based on radiological ap-

pearances, therefore most cases are diagnosed postopera-

tively [5,7] as in our case.

Grossly, MESTK is often a well-circumscribed tumor

with cystic and solid components of variable proportio ns.

According to the literature most tumors have cystic

components of variable proportion [1,12]. However, in

our case there was no a cystic component and it was

completely solid. Mean tumor size reported in the litera-

ture 6 cm [2,4,8,9]. The small size and completely solid

tumors are rarely reported in the literature. Due to that

Figure 1. 4 cm solid tumor on cut section the macroscopic

specimen (asterisk).

Figure 2. Tumor consisting of biphasic components including

tubules embedded in the sindle cell stroma (hematoxylin-

eosin, x200).

fact we could state that our case is unique in many ways

compare to literature reported cases.

The histogenesis of this tumor is unknown, and it has

been proposed that both components of the tumor, stro-

mal and epithelial, are neoplastic. It has been proposed

that a deranged hormonal environment, namely, peri-

menopausal changes or therapeutic hormones with un-

opposed estrogen, induces the proliferation of periductal

fetal mesenchyme. This theory has been supported by the

presence of ER and PR expression in the spindle cells

[2,10]. As we mentioned before the patient had no his-

tory of hormonal therapy. Despite that fact; the tumor

has shown positive reaction to ER and PR immunohis-

E. DEMIRALAY ET AL.

tochemistry proces. Based on this pattern of reactivity we

concluded that our tumor has distinctive character.

Others suggested embryologic hypothesis as mullerian

displacement in the kidney [13]. Another hypothesis to

be considered is that of an epithelial-stromal interaction

in a status of hormonal hyperstimulation [11]. Estrogen

seems to be important, but its role may be to promote

rather than initiate oncogenesis [14]. A case with trans-

location t (1;19) has recently been described [5].

By electron microscopy, it has been shown that some

tubules within the tumor had features of the proximal

tubular epithelium, while other tubules had features of

the thin segment of the loop of Henle, suggesting that the

tubules are entrapped rather than neoplastic [6].

Malign transformation, recurrence, and metastasis are

rare; however, a few cases of malignant MESTK have

been reported in the literature recently [2,4,5,10]. Al-

though malignancy of the epithelial component in these

tumors has not yet been documented, some authors re-

ported stromal malignancy [2,15,16].

MESTK have excellent prognosis and should be dif-

ferentiated especially from renal cell carcinoma. These

tumors do not hold diagnostic characteristics due to that

fact the tumors clinically and radiologically can not be

distinguished.

In conclusion, to distinguish non-diagnostic tumors;

radiological research could be the most appropriate solu-

tion. We hope the suggested area will provide solid re-

sults for the non-diagnostic cases.

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