American Urological Association - Prostatic Stromal Tumors
Prostatic Stromal Tumors
- Spindle cell tumor putatively derived from prostatic specialized stroma.
- Includes pure stromal and mixed epithelial-stromal (phyllodes) tumor.
- Classified into prostatic stromal tumors of uncertain malignant potential (STUMP) and prostatic stromal sarcoma (PSS).
- Phyllodes tumor is classified into STUMP or PSS depending on the stroma (sarcomatous or not).
- Mean age 58 years (range 27-83 years), and include younger patients (>50% with PSS are < 50 years old).
- Majority presents with lower urinary tract or obstructive symptoms.
- Usually occurs as solitary mass.
- STUMP has 4 patterns: degenerative atypia (most common), hypercellular stroma, myxoid, and phyllodes type (stroma + epithelial).
- STUMP lacks significant cellular atypia (except degenerate atypia), mitotic activity, necrosis, or extraprostatic growth (image A) & (image B).
- PSS is more cellular, pleomorphic, mitotically active and has necrosis (image C) & (image D).
- Immunohistochemistry: stromal cells are CD34+ and PR+.
- Epithelial component (only in phyllodes tumor) is PSA+ and PSAP+.
- STUMP has good prognosis since it's mostly confined to prostate, but may recur.
- PSS has high recurrence rate, locally aggressive and can metastasize.
- DDX: other prostatic spindle cell lesions such as BPH (closest mimic of STUMP but nodules multiple with spindle cells following small vessels), sarcomatoid carcinoma (keratin+ since its epithelial), smooth muscle tumors (actin+), GIST (c-kit+), and solitary fibrous tumor.