Surgical Science, 2011, 2, 66-68
doi:10.4236/ss.2011.22014 Published Online April 2011 (
Copyright © 2011 SciRes. 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
Received December 2, 2010; revised January 25, 2011; accepted Februar y 25, 2011
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.
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-
Copyright © 2011 SciRes. SS
Copyright © 2011 SciRes. SS
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
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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