INTRODUCTION {#sec1-1}
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Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors originating from the digestive tract, commonly the stomach.\[[@ref1]\] Extra-GISTs (E-GISTs) are morphologically, immunophenotypically, and histologically similar to GIST but arise outside the gastrointestinal tract.\[[@ref1]\] E-GISTs of the prostate are rare with less than 10 cases reported in the English literature till date.\[[@ref1][@ref2][@ref3][@ref4][@ref5][@ref6][@ref7][@ref8][@ref9]\] We present the case of a 55-year-old male diagnosed with prostatic E-GIST during workup for lower urinary tract symptoms (LUTS) managed with medical therapy.  The present case is the tenth case of prostatic E-GIST.  We also reviewed the relevant literature focusing on the clinical presentation, diagnosis, and the outcomes of E-GIST of the prostate. 

CASE REPORT {#sec1-2}
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A 55-year-old male with history of ischemic heart disease, presented with bothersome LUTS of 6 months duration.  Digital rectal examination revealed massively enlarged nodular prostate and the serum PSA was 3.2 ng/ml.  A standard 12-core transrectal ultrasound guided prostatic biopsy was performed which showed multiple spindle cells which stained positive for c-kit, CD117 and CD34 on immunehistochemistry, consistent with a diagnosis of primary prostatic GIST \[[Figure 1](#F1){ref-type="fig"}\].  Ultrasonography and computed tomography scan of the abdomen and pelvis revealed a massively enlarged (1230 cc) prostate filling the entire pelvic cavity and extending into the rectum and the seminal vesicles \[[Figure 2](#F2){ref-type="fig"}\].  Metastatic workup was negative.  As the patient was a known case of heart disease (New York Heart Association Class III), he was deemed high risk for surgical intervention.  Hence, after surgical/radiation oncologist\'s consult and taking the patient\'s wish, into account, he was started on imatinib mesylate therapy (tyrosine-kinase inhibitor).  The patient reported mild-to-moderate improvement in LUTS (as measured by the decline in the International Prostate Symptom Score) with a reduction in size of the prostatic mass on repeat imaging at 12-month follow-up. 

![ Photomicrograph showing multiple spindle cells disposed in intersecting fascicles](IJU-35-237-g001){#F1}

![ Coronal computed tomography scan image of the patient showing massively enlarged homogeneously enhancing prostate filling almost the entire pelvic cavity](IJU-35-237-g002){#F2}

DISCUSSION {#sec1-3}
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The first case of prostatic E-GIST was reported by Van Der Aa *et al*.  in 2005.\[[@ref1]\] A review of the available case reports and comparison with the present case is presented in [Table 1](#T1){ref-type="table"}.  The age at presentation has varied widely (ranging from 31 to 75 years) in the previously published reports.\[[@ref7]\] The clinical presentation is also variable but generally includes voiding LUTS, hematuria, acute urinary retention, perineal pain, or an abnormal rectal examination.\[[@ref7]\] Usually, the patient has grossly enlarged prostate gland with no/mild elevation in serum PSA levels.  There are no characteristic radiographic features, and the mainstay of diagnosis are the histopathological findings along with immunohistochemistry.\[[@ref1][@ref3][@ref4]\] Majority of the E-GISTs (\>95%) express CD117, whereas around 50%--100% express CD34 antigen.\[[@ref1][@ref3][@ref4]\] In some cases, positive staining for S100 protein, desmin, or smooth muscle actin may also be seen.\[[@ref7][@ref9]\] The present case also had spindle cells which stained positive for CD117 and CD34, which is characteristic of E-GISTs.  Due to rarity of the disease, standard management protocols for E-GISTs are unavailable, and the treatment is based on extrapolated data on GISTs.  For nonmetastatic E-GISTs, radical prostatectomy has been reported, whereas metastatic cases and recurrences have been managed by targeted therapy with tyrosine kinase inhibitors (imatinib mesylate).\[[@ref7]\] Imatinib mesylate therapy is also recommended high-risk patients or patients with advanced disease before and after surgical treatment.\[[@ref7]\] The present case is unique because of the massive size of the prostate, the second largest prostate gland volume ever reported.\[[@ref10]\] E-GISTs confined to the prostate that are managed by radical prostatectomy, seldom reccurd.\[[@ref1]\] Managing prostatic E-GIST with giant prostates (\>500cc) is challenging for the clinicians.  Advanced age and medical comorbidities such as the ischemic heart disease add to the surgical risks.  In the present case, in view of high surgical risk of prostatectomy, a decision was made to start imatinib mesylate therapy after consulting medical oncologist. 

###### 

Review of the published case reports on prostate E-GIST

  Author (year)                           Age   Presenting complaints                 Prostate size (cm)   S.PSA (ng/ml)   Mets       Treatment                          Follow up (months)   Outcome
  --------------------------------------- ----- ------------------------------------- -------------------- --------------- ---------- ---------------------------------- -------------------- ---------------------
  Van Der Aa *et al*.\[[@ref1]\] (2005)   49    AUR                                   14.2 x 9.6 x 14.0    1.36            (+)Liver   TKI                                25                   Reduced mass volume
  Lee *et al*.\[[@ref2]\] (2006)          75    AUR and dysuria                       6.7×5.6×5.5          1.36                       RP                                 6                    No recurrence
  Yinghao et al.\[[@ref3]\] (2007)        49    Pain in anal region                   8.5×7.0×6.0          1.1             (-)        RP                                 14                   No recurrence
  Ou *et al*.\[[@ref4]\] (2013)           39    Voiding LUTS and dysuria              10                   0.87            (-)        RP                                 24                   No recurrence
  Liu *et al*.\[[@ref5]\] (2014)          55    dysuria                               10×10.5×9.5          2.01            (-)        RP + TKI                           12                   No recurrence
  Zhang *et al*.\[[@ref6]\] (2014)        31    LUTS, hematuria                       6.0×6.1×6.5          1.1             (-)        TKI                                3                    Died
  Etit *et al*.\[[@ref7]\] (2018)         56    Pain in anal region                   6                    1.1             (-)        RP                                 49                   No recurrence
  You *et al*.\[[@ref8]\] (2018)          66    Intermittent defecation abnormality   7.6×7.6×8.7          1.61            (-)        RP                                 36                   No recurrence
  Almagharbi *et al*.\[[@ref9]\] (2018)   84    Recurrent AUR                         17\. × 16×5          5.4             (-)        Trans-vesical open prostatectomy   \-                   No recurrence
  Present case                            55    Voiding LUTS                          18.5 x 16 x 6        3.2             (-)        TKI                                12                   No recurrence

E-GIST-extraintestinal gastrointestinal stromal tumor; AUR-acute urinary retention; PSA-prostate specific antigen; TKI-tyrosine kinase inhibitor; LUTS-lower urinary tract symptoms; RP-radical prostatectomy

CONCLUSION {#sec1-4}
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Given the rarity, E-GISTs should be included in the differential diagnosis of patients presenting with LUTS as it may influence the treatment decisions. 

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### Declaration of patient consent {#sec3-1}

The authors certify that they have obtained all appropriate patient consent forms.  In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal.  The patients understand that their names and initials will not be published and due effort will be made to conceal their identity, but anonymity cannot be guaranteed. 

**Financial support and sponsorship:** Nil. 

**Conflicts of interest:** There are no conflicts of interest.