Stromal Tumor of Uncertain Malignant Potential (STUMP) of The Prostate: A Case Report
*Rahman DA,1 Kabir AN,2 Pradhan B,3 Begum F,4 Kamal M5
Stromal tumor of uncertain malignant potential (STUMP) of the spindle cell lesion of prostate is rare tumor with a variable and unpredictable clinical course. The pathological diagnosis of STUMP is sometimes confused with the stromal proliferations present in BPH and stromal sarcoma, the distinction may be difficult. Owing to the rarity of these tumors, the classification, expected clinical course, and treatment recommendations are still a matter of debate. We report a case of a 45 years old man presented with pelvic mass and acute retention of urine which is diagnostically challenging. This is probably the first reported case of STUMP in Bangladesh.
[Journal of Histopathology and Cytopathology, 2019 Jan; 3 (1):53-57]
Keywords: Prostate, Stromal tumour
Prostatic stromal tumors of uncertain malignant potential (STUMPs) are rare tumors characterized by an atypical stromal proliferation unique to the prostate. This entity has previously been classified under a variety of names including phyllodes tumor of the prostate, atypical stromal hyperplasia, cystosarcomaphyllodes, and cystic epithelial-stromal tumor. Four distinct patterns of stromal proliferations within STUMPs have been described. The distinction between STUMP from BPH and stromal sarcoma, may be difficult.1 Immunohistochemical results show that STUMP and stromal sarcomas both are typically positive for CD34 and progesterone receptor(PR) may be used to distinguish them from other prostatic mesenchymal neoplasms. STUMPS typically react positively with smooth muscle actin, whereas prostatic stromal sarcomas react negatively. In general, patients with a diagnosis of STUMP have a good prognosis, as most cases are confined to the prostate. However, it should be noted that some cases of STUMP may have the potential to undergo malignant transformation, or may be intimately associated with stromal sarcoma (SS). The appropriate treatment of STUMPs is unknown. When these lesions are extensive or associated with a palpable mass definitive therapy may be considered. There is still considerable debate regarding the definition, pathology and prognosis of this group of lesions.
*Dr. DM Arifur Rahman, Assistant Professor, Department of Pathology, TMSS Medical College, Bogura email@example.com
Dr. AKM Nurul Kabir, Associate Professor, Department of Pathology, BSMMU, Shahbag, Dhaka.
Dr. Birendra Prodhan, Pathologist Jigme Dorji Wangchuk National Referral Hospital. Thimphu, Bhuta.
Dr. Ferdousy Begum. Associate Professor, Department of Pathology, BSMMU, Shahbag, Dhaka.
Professor M Kamal, Professor, Department of Pathology, BSMMU, Shahbag, Dhaka.
A 45 years old male was referred Bangabandhu Sheikh Mujib Medical University from a peripheral medical college hospital after having done preliminary investigations there. He was admitted to that hospital following acute retention of urine about seven months back. Since then he was catheterized. Over the past two years, he had developed progressive dysuria, increased frequency of micturition, narrow stream of flow and incomplete voiding for which he consulted doctors on couple of occasions and was managed conservatively. Ultrasonography at the hospital revealed a large pelvic mass. USG guided FNA was performed and it was reported as mesenchymal tumor of fibrohistiocytic origin of benign potential. Thereafter, he was referred to BSMMU with the hope of better management. At BSMMU, thorough histories were taken and examinations were done. Among those the most significant findings include the digital rectal examination which revealed a growth on the anterior wall of rectum about 2 cm from the anal verge. PSA was raised (11.9 ng/ml) and CEA was within normal limit (6.16 ng/nl). PET-CT was done and it revealed a large prostatic neoplasm. However, core needle biopsy report was suggestive of GIST with neural differentiation or neurofibroma. With this background laparotomy was done and the tumor mass was enucleated. The tissue was sent for histopathology. Grossly, the specimen consisted of a nodular piece of tissue measuring about 9x8x7 cm. Sectioning showed mostly solid grey white area and partly small cystic spaces containing clear fluid. Microscopically, it revealed stromal proliferation containing oval to spindle shaped cells with scanty cytoplasm along with benign prostatic glands. Some of the tumor cells were bizarre looking and showed degenerative atypia. However, mitosis was rare. No necrosis was seen either. Following the histopathological diagnosis, out of academic interest and as per the surgeon’s instruction to rule out GIST, Immunohistochemistry (IHC) was done at BSMMU. CD 34, SMA, PR were positive and CD117 was negative.
Figure 2. Macroscopic view (A) H&E x 100, (B) Masson Trichromex 400, (C) SMA x 400 (D), PR x 400 (E), CD117 x 200 (F).
STUMP is an exceedingly rare tumor characterized by an atypical, unique stromal proliferation of the prostate. STUMPs have been reported to occur between the ages of 27 and 83 years, with a median age of 58 years and a peak incidence in the sixth and seventh decades.2,3 Patients presented most commonly with urinary obstruction, followed by abnormal rectal examination, hematuria, hematospermia, rectal fullness, palpable rectal mass or elevated serum prostate specific antigen (PSA) levels. Prostatic stromal lesions that were not obvious sarcomas have been designated STUMP reflecting theuncertain nature of the clinical course in affected patients.4 Distinguishing between STUMP and prostatic stromal sarcoma is often morphologically difficult. Parameters used to differentiate these two processes include cellularity, mitotic activity, necrosis, and extension into surrounding organs.5 The etiology and pathogenesis of STUMP is unknown, and no confirmed risk factors have been identified. A small number of cases are diagnosed in the setting of a concurrent prostatic adenocarcinoma.5 STUMP can occur at a younger age than BPH, predominantly involve the peripheral zone, and often adhere to the rectum.3
Grossly, STUMP may be white, tan, or yellow and range from solid and firm to partially cystic and multiloculated. The lesions range in size from microscopic up to 15 cm with small or large smooth-walled cysts. The cyst contents may be serous, mucinous, or sanguinous.3,6 These tumors may involve either the transition zone or the peripheral zone and mayrange in size from microscopic lesions (which are typically incidentally found) to large, cystic lesions up to 15 cm in size.3
Gaudinet al classified STUMPs into four distinct histologic patterns by the degree of stromal cytologic atypia, and the presence and appearance of a nonneoplastic epithelial component. They are: Degenerative atypia pattern, Myxoid pattern, Phyllodes-type growth pattern, Hypercellular stroma pattern. Two or more of these patterns may coexist in the same specimen.2
Differential diagnosis and ancillary studies
In transurethral resections, prominent stromal hyperplasia of BPH may get confused with STUMP. Presence of multinodularity, lack of intermingling glands, uniform spindle cells, prominent blood vessels, and presence of chronic inflammatory cells favor BPH. C-kit or ALK-1 immunoreactivity suggests a specific diagnosis of GIST or inflammatory myofibroblastic tumor respectively. Definitive diagnosis in small needle biopsy may not be feasible and may need an excision for definitive classification.
Both STUMP and PSS typically express CD34, progesterone receptor (PR) and vimentin. Progesterone receptor is frequently present while estrogen receptor is infrequently expressed. Desmin, HHF-35, and smooth muscle actin are often positive in STUMP but negative in PSS. In a subset of cases, pancytokeratin and CAM5.2 stains are focally expressed.7
Treatment and prognosis
STUMP presents a significant challenge for patient management. While many will prove to be indolent in nature, their behavior is unpredictable. In cases where STUMP has behaved aggressively, dedifferentiated, or coexisted with sarcoma, no correlation with a specific histologic subtype or other risk factor has been identified. The prognosis of STUMP is equally variable. One retrospective study found that in patients who did not undergo definitive resection, the tumor recurred in 46% of cases. In some cases, the tumor recurs several times, requiring multiple procedures over time.3 Two of the three patients in these reports died of their illness.8-10
In summary, we report a case of prostatic STUMP that was difficult to diagnose. STUMP is rare and can be histologically misdiagnosed as BPH. It has the potential to transform into SS. Therefore, STUMP should be managed aggressively with radical resection.
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- Gaudin PB, Rosai J, Epstein JI. Sarcomas and related proliferative lesions of specialized prostatic stroma: a clinicopathologic study of 22 cases. The American journal of surgical pathology. 1998 Feb 1;22(2):148-62.
- Herawi M, Epstein JI. Specialized stromal tumors of the prostate: a clinicopathologic study of 50 cases. The American journal of surgical pathology. 2006 Jun 1;30(6):694-70.
- Eble JN, Sauter G, Epstein JI, Sesterhenn IA, eds. Pathology and Genetics ofTumours of the Urinary System and Male Genital Organs. Lyon, France: IARC Press; 2004. The World Health Organization Classification of Tumours; vol 7.
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- Watanabe M, Yamada Y, Kato H, Imai H, Nakano H, Araki T, Shiraishi T. Malignant phyllodes tumor of the prostate: retrospective review of specimens obtained by sequential transurethral resection. Pathology international. 2002 Dec 1;52(12):777-83.