How to cite this article:Ktari k, Hamdouni W, Moez H, Saidi R, Zakhama A, Saad H. Mixed Epithelial and Stromal Tumor of the Kidney Case report.
002 JOJ uro & nephron. 2018; 5(5): 555675. DOI: 10.19080/JOJUN.2018.05.555675
In recent years, a rare distinctive kidney tumor composed of a mixture of stroma and epithelium with solid and cystic architecture has been recognized, which has to be distinguished from other renal neoplasms. The term mixed epithelial and stromal tumor was first introduced by Michal and Syrucek in 1998. The vast majority of cases show a benign course without tumor recurrence. Here, we present a case of this entity, found incidentally.
Keywords: Kidney; Benign; Mixed epithelial and stromal tumor
Abbreviations: MESTK: Mixed Epithelial and Stromal Tumor of Kidney; KUB: Kidney Ureter Bladder; RCC: Renal Cell Carcinoma
Mixed epithelial and stromal tumor of kidney (MESTK) is a rare complex renal neoplasm, composed of stromal and epithelial elements, and a mixture of cystic and solid areas [1,2]. It was originally described in 1973 by Block et al. as a congenital mesoblastic nephroma.
The name mixed epithelial and stromal tumor of the kidney “MESTK” was first introduced by Michal and Syrucek in 1998 . Cystic hamartoma of the renal pelvis, leiomyomatous renal hamartoma, adult mesoblastic nephroma, multilocular renal cyst with Mullerian-like stroma, and solid and cystic biphasic tumor were designations for this condition in the past [1,3]. Recent advances in molecular-level studies of the pathogenesis have resulted in an increased awareness of this type of renal tumor. In this article, we present a case of this entity, found accidentally and a review of the literature.
A 48-year-old woman, she is menopaused, has ten children and has a history of oral contraceptive use during five years. She was followed at our service since 2000 for management of recurrent bilateral nephritic lithiasis. She had presented to our clinic with left intermittent flank pain. Physical examination was unremarkable, except mild left flank pain. Her routine
blood investigations were normal, routine urine analysis revealed no hematuria.
Kidney-ureter-bladder (KUB) radiograph had showed calcification in the left kidney. Intravenous urography showed bilateral and symmetrical secretion and renal excretion, with delayed opacification of the renal pelvis and the ureter to the left side, up to 10 minutes, the left kidney is increased in size with good corticosinusal index, with expansion on the upper calyx (Figure 1).
The patient had a dorsal lumbotomy.!
On surgical exploration there was incidentally a whitish solid nodule of 2 cm in diameter, round shaped, and well circumscribed with a thin fibrous capsule. There were no signs of infiltrative
growth into the surrounding renal parenchyma. The tumor was
situated in the renal parenchyma and compressed the adjacent
calyceal system. A lumpectomy was performed.
Grossly the tumor had a solid appearance without cyst
formation, white color, soft to elastic consistency without
hemorrhage and necrosis.
Histologically (Figure 2), the tumor was biphasic comprising
epithelial and stromal elements. It includes microcysts and
tubules, and ovarian-like stroma. The epithelial component
shows flattened cuboidal or hobnail cells, their cytoplasm
ranges from clear to pale eosinophilic. The architecture of
the microcysts varied from simple microcysts with abundant
stroma between them, to densely packed clusters of microcysts
to complex branching channels. The stroma consists of variably
cellular proliferation of spindle cells with plump nuclei and
abundant cytoplasm. Areas of myxoid stroma and smooth muscle
cells also identified at places. No dysplasia increased mitotic
activity, or tumor necrosis as signs for malignant transformation
were observed. The immunohistochemical investigations was
not performed. The final histopathological diagnosis was MESTK
(mixed epithelial and stromal tumor of the kidney).
The postoperative course was uneventful.
The patient has received regular follow-up at our out-patient
department. No evidence of tumor recurrence has been found
after 10 years.
MESTK is a distinct category of renal neoplasm. Patients’
ages range from 19 to 84 years (mean, 46 years), with a
female/male incidence ratio of 10-6:1. It often affects women
with prolonged estrogen exposure and rarely occurs in male
patients who have undergone androgen deprivation therapy.
Most patients typically present with flank pain, a palpable
abdominal or flank mass, hematuria, or symptoms related to
genitourinary infections, although up to 25% of tumors are
identified incidentally [1,2,4,5]. MESTK is typically a centrally
located, tan to yellow, well-circumscribed, solid cystic lesion,
with 1.7 to 20cm being the largest. In this case, owing to loss of
the perirenal fascia tension, a CT scan showed that the surgical
specimen was larger than the size of the mass. Microscopically,
the MESTK contained an admixture of stroma and epithelial
lined large cysts, microcysts, and tubules. In general, ER, PR,
CD10, Vimentin, Desmin, SMA, and inhibin expression was seen
in the stromal component. HMB-45, S-100, CD99, CD117, and
CD34 stains were negative. The epithelial components were
positive for CK7, PCK, cytokeratin AE1/3, Ulex europaeus, and
MESTKs have certain features in imaging and are more
common in Bosniak III/IV. Most MESTKs can be described as well
circumscribed in the renal pelvis or protruding from the cortex,
and show multiseptate cystic renal masses with thick septa and
solid components. The emphasis here is on enhancing the image
of the solid components with the delayed enhancement during
the nephrographic phase in the contrast-enhanced CT images.
The different extent of the delayed enhancement may depend
on the spindle cell components of these masses, which exhibit
variable patterns and cellularity ranging from paucicellular
fibrosis to densely cellular areas [7,8].
However, the pathogenesis of MESTK is still not clear. There are
several theories to explain the possible histogenesis mechanism.
One hypothesis is the presence of multidifferentiation potential
fetal primitive mesenchyme or metanephric blastema in the
kidney, which may be an epithelialestromal interaction given
its status of hormonal hyperstimulation, which may then cause
the proliferation to form a mass [3,9]. Another hypothesis
is the abnormal migration of ovarian stromal cells during
embryogenesis. Because of the close proximity of mesonephric
ducts and Mullerian ducts during the 4th week of development,
ovarian stromal cells could become incorporated in the ureteric
bud and metanephric mesoderm. These cells may become
activated in the steroid hormonal stimulation, secrete paracrine
factors, and induce proliferation of the
adjacent epithelium . Above all, although the histogenesis
of MESTK is unknown, in view of the frequent expression of ER
and PR in the stromal component and the existence of ovariantype
stroma, both theories suggest that the steroid hormones
might play a role in the evolution of these tumors.
Tickoo et al.  believed that ER/PR-positive stromal
proliferation can be present in some nonneoplastic kidneys
and the part of neoplastic kidneys away from the tumor, such
as ureterepelvic junction stenosis, benign multilocular cyst,
benign ureteric stricture, acquired cystic disease-associated
renal cell carcinoma (RCC), urothelial carcinoma ureter,
urothelial carcinoma bladder, chromophobe RCC, clear cell
RCC, except for MEST and cystic nephroma. However, they
observed that the diseases mentioned above had a common
findingda generalized or segmental hydronephrosis, or tumor
compression-related focal obstruction. Based on this finding,
they reached a conclusion that renal obstructive changes may
represent a metaplastic change in the renal interstitial cells
surrounding these obstructed epithelial structures. Moreover,
the ER/PR stoma seen in association with renal tumors may also
be a secondary (metaplastic) response to their cystic epithelial
components and not necessarily a neoplastic constituent.
Similarly, using electron microscopy, Picken and Fresco 
found that the tubules in MESTK are entrapped rather than
neoplastic. To summarize, we postulate that the histogenesis
of MEST results not only from the stimulation of the hormones,
which cause the proliferation to form a mass, but also that the
cysts’ compression-related obstructive changes may likewise
play an important role in its development. Through a synergistic
action, the MESTK may grow larger and lead to further clinical
symptoms. We argue that this requires further study.
Tumor spillage or positive surgical margins are presumably
risk factors for local recurrence . Hence, complete surgical
resection is the preferred treatment for MESTK. According to the
patient’s condition, partial or complete nephrectomy was chosen.
And when a partial nephrectomy was performed to exclude a
positive margin, an intraoperative frozen section was helpful
. Because the tumor was rare and the preoperative diagnosis
was difficult, we could not rule out malignancy. At this point, the
treatment of choice was nephrectomy and the complete removal
of the tumor. For the diagnosis, preoperative biopsy may cause
the cyst to rupture and increase the risk of recurrence. Therefore,
preoperative biopsy should be conservative. In terms of clinical
behavior, rare aggressive behavior has been reported ;
however, most cases of MESTK exhibit a benign histologic picture
and clinical course, and both neoplasms are benign and surgical
excision results in restoration . If diagnosed preoperatively,
for the patient who has a high risk for an operation, follow-up
without any operation might be an alternative.
MESTK is relatively rare, usually presents in perimenopausal
women as a partially cystic mass, and its growth may be influenced
by hormones. Any cystic tumor presenting in perimenopausal
women should undergo the same series of tumor surveys as for
malignant tumors. A mixed epithelial and stromal tumor of the
kidney should be considered one of the possibilities. Therefore,
pathogenesis and preoperative diagnosis should be further