Which histologic findings are characteristic of stromal tumors of uncertain malignant potential (STUMP)?

Updated: Jan 04, 2021
  • Author: Fabio R Tavora, MD, PhD; Chief Editor: Liang Cheng, MD  more...
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Stromal tumors of uncertain malignant potential (STUMP) are stromal proliferations characterized by hypercellularity and/or cytologic atypia without evidence of true sarcomatous transformation. [22] The atypical stromal cells have enlarged nuclei with nuclear hyperchromasia and occasional multinucleation. Few or no mitotic figures are present in reported cases of STUMP, and the occurrence of atypical mitoses should make the pathologist highly suspicious of a prostatic stromal sarcoma or other sarcomas involving the prostate. An association with prostatic glands is common, which are histologically benign.

Four different patterns of STUMP have been described, as follows:

  • Degenerative atypia with hypercellularity

  • Degenerative atypia without hypercellularity

  • Phyllodes tumor

  • Myxoid pattern, which is set apart by extensive overgrowth of myxoid stroma that resembles the stroma of benign prostatic hyperplasia.

Investigators recently identified a novel round cell histological pattern of STUMP. Tumors with round cell morphology may be misidentified as gastrointestinal stromal tumor, prostatic adenocarcinoma, or benign prostatic hyperplasia. [1, 22]

STUMPs may have a mixture of patterns.

Histologic pattern recognition is helpful in the identification of these lesions, but there is no association of histologic pattern with aggressive local growth or progression to sarcoma. Although the seminal paper on the categorization of STUMP argued that a subset of these lesions may reflect hyperplastic processes, criteria allowing separation of some atypical hyperplastic lesions from STUMP have not been established. [3]

Nagar and Epstein systematically described the epithelial proliferations occurring in STUMP and suggested from their findings that, within STUMPs, there is epithelial-mesenchymal crosstalk, as has been described in benign prostate and prostatic carcinogenesis. According to the authors, in unusual cases of STUMP, the epithelial proliferation may predominate to the extent that it can mask the diagnosis of STUMP. [23]

In the Nagar and Epstein study, the most common abnormalities were glandular crowding in 35 of 70 cases (50%), a very prominent basal cell layer in some glands in 32 of 70 cases (46%), and prominent papillary infolding in 13 of 70 cases (19%). Other epithelial changes within the STUMP included cystically dilated glands; basal cell hyperplasia; urothelial metaplasia; squamous metaplasia; cribriform hyperplasia; adenosis; and high-grade PIN, low-grade PIN, and partial atrophy. The glandular component of STUMP was histologically normal in 12 (17%) cases. [23]

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