Review of Specialized Prostatic Stromal Tumors

By Bahram Robert Oliai, M.D.

 

This month’s newsletter begins with the presentation of a most interesting case recently sent to us by one of our clients, Dr. Cordell Nwokeji of Premier Urology in Kingwood, Texas.

Case Presentation:  A 57 year old male with a PSA of 2.3 ng/dL presented to his urologist with a palpable prostatic nodule at the left base for which he underwent sextant needle biopsy including several biopsies of the left base nodule. Biopsies of both the left base and left base nodule demonstrated a similar peculiar lesion composed of mildly hypercellular stroma with spindled cells sporting bizarre, enlarged, hyperchromatic, pleomorphic nuclei infiltrating among benign glands. These cells exhibiting “smudgy” chromatin with degenerative cytologic atypism reminiscent of the so-called “ancient change” sometimes seen in benign nerve sheath tumors (Fig. 1). A succinct panel of immunostains demonstrated that the lesional cells expressed CD34, ER, and PR with a low Ki-67 proliferation rate (Figs. 2-5) and were negative for low molecular weight cytokeratin, smooth muscle myosin, S100, CD117 (c-kit), myogenin, and ALK-1.

 

Diagnosis: Specialized Prostatic Stromal Tumor of Uncertain Malignant Potential (STUMP)

Following the diagnosis the patient underwent a radical prostatectomy which revealed a 2 cm STUMP at the left base and an adjacent incidental focus of prostatic adenocarcinoma, Gleason score 3+3=6.

Prostatic Stromal Tumor of Uncertain Malignant Potential (so-called STUMP)

What is a STUMP? How are they related to prostatic stromal sarcomas? What are the implications for the patient who receives this diagnosis? What is the best way to treat a patient with a diagnosis of prostatic STUMP made on needle biopsy? These are some of the questions which I will address in this month’s newsletter. 

STUMPs are a distinct group of lesions arising from the specialized, hormonally responsive stroma of the prostate. Patients can range in age, but generally present in the sixth or seventh decade of life with lower urinary tract symptoms and abnormal digital rectal examination. In contrast to benign prostatic hyperplasia (BPH) which tends to involve the central zone, STUMPs generally involve the peripheral zone of the prostate and can even adhere to the rectum.

Histologically there are four main patterns of STUMP. The degenerative atypia pattern of STUMP (current case) shows cytologically atypical cells with smudgy chromatin snaking through benign glands like a water moccasin making its way through a patch of lilly pads (Fig. 6). The hypercellular pattern has features very similar to the stroma of BPH but with greater cellularity, making this pattern extremely difficult to diagnose on needle biopsy (Fig. 7). The myxoid pattern demonstrates an overgrowth of cytologically bland myxoid stroma and may lack associated glands (Fig. 8). Finally, a phyllodes-type growth pattern may be seen very similar to phyllodes tumor of the breast (Fig. 9). STUMPs can also show a mixture of these various patterns within the same lesion.

 

Relationship to Prostatic Stromal Sarcoma

Although there can be an overlap between features of STUMPs and prostatic sarcomas, prostatic stromal sarcomas tend to differ from STUMPs in that they often show greater pleomorphism, marked hypercellularity, necrosis, and increased mitotic activity (Fig. 10). While in some cases STUMPs may represent incidental findings, STUMPs can eventually dedifferentiate into high grade sarcomas. Additionally, one can have features of a STUMP on transurethral resection or biopsy while elsewhere within the same lesion there is unsampled sarcoma. In fact, 7 of 14 specialized prostatic stromal sarcomas reviewed by Herawi and Epstein were associated with STUMPs (either prior to the development of sarcoma or within the same lesion in different foci). Due to this “tip of the iceberg phenomenon”, when one diagnoses a STUMP it is very important to communicate the potential risk the diagnosis carries.

 

 

Differential Diagnosis

Given the rare nature of STUMPs and prostatic stromal sarcomas, other entities which enter in the differential diagnosis (both malignant and benign) should be excluded. These include gastrointestinal stromal tumors (GIST), nerve sheath tumors, carcinoma, solitary fibrous tumors, smooth muscle tumors, rhabdomyosarcoma, inflammatory myofibroblastic tumor, and even synovial sarcoma. Immunohistochemistry is essential in ruling out these possibilities and establishing a diagnosis of STUMP/prostatic stromal sarcoma (Table 1).

Follow-up/Treatment

The dilemma in dealing with STUMPs lies in their unpredictable behavior. In some cases, STUMPs may represent a focal incidental lesion of little clinical significance. On the other hand, STUMPs may also be extensive tumors that can rapidly recur leading to urinary obstruction. As noted by Herawi and Epstein, there are also rare examples of dedifferentiation of STUMPs into high grade stromal sarcomas. Finally, one can have STUMP on transurethral resection or needle biopsy where there is unsampled stromal sarcoma in the prostate. Therefore it is imperative that prostatic STUMPs are identified and patients carefully followed.

Management options which have been advocated include additional sampling in attempts to identify the extent of the lesion and to rule out a higher grade component, close clinical follow-up (especially in older men) where the lesion is focally present, and nonpalpable and radical prostatectomy, especially in younger men where there is a palpable lesion or a lesion is seen on imaging and the lesion is felt to be more extensive.

Reference(s):

1. Herawi M and Epstein JI. Specialized Stromal Tumors of the Prostate: A Clinicopathologic Study of 50 Cases. The American Journal of Surgical Pathology. 2006; 30(6): 694-704.

Acknowledgments:

I would like to thank Dr. Cordell Nwokeji of Premier Urology in Kingwood, Texas for sending us the case on which this newsletter was based, and for providing us with the follow-up information on this patient.

Special thanks to Dr. Jonathan Epstein for his permission in using images from Epstein JI, Xang XJ. Prostate Biopsy Interpretation, Philadelphia: Lippincott, Williams & Wilkins, 2002.

 

Date of last revision: April 2009.