Smooth Muscle Tumor of Uncertain Malignant Potential (STUMP): A Comprehensive Multidisciplinary Update

Abstract

Background and Objectives: The uterine smooth muscle tumors of uncertain malignant potential (STUMP) are tumors with pathological characteristics similar to leiomyosarcoma, but that do not satisfy histological criteria for leiomyoma. These are problematic lesions with intermediate morphologic features; thus, diagnosis and treatment are difficult. This narrative review aims to review data in the literature about STUMPs, particularly focusing on management and therapeutic options and strategies for women who desire to preserve fertility. Material and Methods: authors searched for "uterine smooth muscle tumor of uncertain malignant potential" in PubMed and Scopus databases, from 2000 to March 2023. Pertinent articles were obtained in full-text format and screened for additional references. Only articles in English language were included. Studies including full case description of patients with histopathological diagnosis of STUMP in accordance with Stanford criteria were included. Results: The median age was 43 years old. Symptoms are similar to those of leiomyomas, with a mean diameter of 8.0 cm. Total hysterectomy with or without bilateral salpingo-oophorectomy is the standard care for women if fertility desire is satisfied. Myomectomy alone can be considered for young patients. Although these tumors have not a high malignant potential, several studies described recurrence and metastases. Conclusions: STUMPs are complex uterine smooth muscle tumors, with a rare but reasoned clinical-diagnostic management. Considering the high clinical and histological complexity of these tumors, high level of expertise is mandatory.

Keywords: STUMP; leiomyosarcoma; smooth muscle tumors of uncertain malignant potential; uterine fibroids; uterine mesenchymal tumors.

Figure 1

Image of a STUMP removed in laparotomy on a 39-year-old patient, having a well-circumscribed and non-encapsulated appearance.

Figure 2

Image of another STUMP of consistent volume, removed in laparotomy in a young patient of 32 years; it appears soft in texture.

Figure 3

Smooth Muscle Tumor of Uncertain Malignant Potential (STUMP). (A) Hematoxylin and Eosin (H & E)-stained section at 40× magnification showing bundles of smooth muscle cells. (B) H & E-stained section at 100× showing tumor cells with diffuse moderate-to-severe atypia. (C) H & E section at 200× revealing spindled cells showing atypia and pleomorphism. (D) H & E section at 400× depicting atypia and occasional mitosis. There was no tumor necrosis and mitotic count was less than 10/10 HPFs, consistent with the diagnosis of STUMP.

Figure 4

Histological magnification at 2.5×. The presence of necrosis that is difficult to classify: ischemic or coagulative.

Figure 5

Image on the left (at magnification 10×) shows positive staining for SMA (smooth muscle actine); Image on the right (magnification 20×) shows positive staining for Caldesmon (immunoprofile characteristic for smooth muscle tumors).

Figure 6

Histological magnification 20×: proliferative index (expression of ki-67) is variable and often not contributory; in this case, 1%.

Figure 7

Image on the left (at magnification 40×) shows significant cytologic atypia. Image on the right shows low mitotic activity (in this particular case, 5–10 mitosis/10 HPF).

Figure 8

Histologic magnification 5×: This image shows sharp tumor demarcation (no infiltrative growth).